Refactored GradleLocation to at least have a chance to solve the issue described in the comments of issue #118.
Minor refactoring in GradleModelLoader.
Added convenience methods to deserialize objects from file (and write it).
Added stub for SerializedNbGradleModels.
GradleModelLoader should now read saved file from the persistent cache (though it is pointless now because it is not saved).
SerializedNbGradleModels returns null model for now.
Models are now saved into the disk (though the serialized form is currently a dummy implementation so it is not yet useful).
NbGradleProjectTree is now serializable.
NbGradleMultiProjectDef is now serializable.
Removed extra empty line.
NbGenericModelInfo is now serializable.
Fixed some NB warnings in NbGradleMultiProjectDef.
Removed comment from since it is no longer meant to be serializable directly.
SerializedNbGradleModels now actually stores the information needed.
SerializedNbGradleModels now supports null models.
SerializedNbGradleModels can now deserialize models.
SerializedNbGradleModels is now more forgiving when an extension's model is not serializable.
Fixed an NPE when trying to save models.
The cache directory is now actually called cache.
Saving models to persistent cache even if multiple projects get evaluated in a single call.