to_dict() and from_dict() functionality for Coregionalize Kernel and MixedNoise Likelihood class, appveyor CI resurrected (#951)

This PR adds two main things to GPy:
- to- and from-dict functions for the kernels listed belop
- a fix for the appveyor CI
Please see the squashed commit messages listed below.
Authors: @gehbiszumeis @ppk42 respectively
Reviewer: @ekalosak 

---
* new: added to_dict() method to Coregionalize kernel class

* new: added to_dict() method to MixedNoise likelihood class

* fix: made Y_metadata dict content serializable

* fix: typo

* added additional needed parameters to to_dict() method for Coregionalize kernel + added _build_from_input dict method

* new: added possibility to build MixedNoise likelihood from input_dict

* Y_metadata conversion from serializable to np.array when loading from dict

* fix: rework Y_metadata part for compatibility with unittests !minor

* conda cleanup in appveyors pipeline

* conda clean up after conda update

* conda clean before conda update

* try pinning packages for conda

* revert all conda changes

* conda clean all (not only packages)

* use conda update anaconda

* pin conda package

* pin conda package

* try installing charset-normalizer beforehand

* try to get from conda-forge

* revert all conda changes

* Try to fix the conda update challange.

See: https://community.intel.com/t5/Intel-Distribution-for-Python/Conda-update-Conda-fails/td-p/1126174

It is just a try for a different context/(conda version).

* Still fixing build error on appveyor

I also use a newer miniconda version for greater python versions.

* Update appveyor.yml

Thinking it over it decided to use miniconda38 for all python versions unless python 3.5.

* revert miniconda versioning changes

* adjust GPy version in appveyor.yml

* 1st attempt bring the appveyor build to life again

* #955 fixing ci build on appveyor

After bringing the miniconda env to work again, the wrong matplotlib version was used. This commit should fix that.

* #955 Fix CI build

Freezing numpy and scipy was a bad idea.
I freeze matplotlib  dependend  on the python version only.

* add: built_from_dict method for White Kernel

Co-authored-by: Peter Paul Kiefer <ppk42@users.noreply.github.com>
Co-authored-by: Peter Paul Kiefer <dafisppk@gmail.com>

GPy/core/gp.py

@@ -134,9 +134,10 @@ class GP(Model):
         if self.mean_function is not None:
             input_dict["mean_function"] = self.mean_function.to_dict()
         input_dict["inference_method"] = self.inference_method.to_dict()
-        #FIXME: Assumes the Y_metadata is serializable. We should create a Metadata class
+        # TODO: We should create a Metadata class
         if self.Y_metadata is not None:
-            input_dict["Y_metadata"] = self.Y_metadata
+            # make Y_metadata serializable
+            input_dict["Y_metadata"] = {k: self.Y_metadata[k].tolist() for k in self.Y_metadata.keys()}
         if self.normalizer is not None:
             input_dict["normalizer"] = self.normalizer.to_dict()
         return input_dict
@@ -162,9 +163,12 @@ class GP(Model):
             input_dict["mean_function"] = mean_function
         input_dict["inference_method"] = GPy.inference.latent_function_inference.LatentFunctionInference.from_dict(input_dict["inference_method"])
 
-        #FIXME: Assumes the Y_metadata is serializable. We should create a Metadata class
+        # converts Y_metadata from serializable to array. We should create a Metadata class
         Y_metadata = input_dict.get("Y_metadata")
-        input_dict["Y_metadata"] = Y_metadata
+        if isinstance(Y_metadata, dict):
+            input_dict["Y_metadata"] = {k: np.array(Y_metadata[k]) for k in Y_metadata.keys()}
+        else:
+            input_dict["Y_metadata"] = Y_metadata
 
         normalizer = input_dict.get("normalizer")
         if normalizer is not None:

GPy/core/parameterization/variational.py

@@ -106,7 +106,7 @@ class VariationalPosterior(Parameterized):
         self.link_parameters(self.mean, self.variance)
         self.num_data, self.input_dim = self.mean.shape
         if self.has_uncertain_inputs():
-            assert self.variance.shape == self.mean.shape, "need one variance per sample and dimenion"
+            assert self.variance.shape == self.mean.shape, "need one variance per sample and dimension"
 
     def set_gradients(self, grad):
         self.mean.gradient, self.variance.gradient = grad