Remove duplication between methods loading weights and cleanup code (#…

…326)

* Remove unnecessary "run" function usages

* Remove unnecessary "this" qualifier usages

* Simplify getting keras version from the weights file

* Remove duplication between methods loading weights for all or a subset of layers

* Simplify loading weights for frozen layers

* Reorder methods

* Do not mark the model as initialized when the format is unknown

* Extract a single method for loading model weights

* Allow using loadWeightsForFrozenLayersByPathTemplates function for any GraphTrainableModel