Minor: Remove commented out code
Rename: OverridingUtil#filterOverrides -> filterOutOverridden to be more precise
Add filterOutOverriding to OverridingUtil
Add new functionality to "Change signature" refactoring

Extract single point of entry for all change signature refactorings and fixes (remove parameter, add parameter)
Change signature now affects overriding functions as well
Promt the user whether he wants to refactor base function(s) or the selected one if appropiate
Fix a problem with descriptorToDeclaration in JetChangeSignatureHandler
Rename: JetFunctionPlatformDescriptor -> JetMethodDescriptor
Eliminate redundant descriptorToDeclaration call from factory for "Change signature" quick fixes
Show error hint when trying to refactor synthesized function
Prefer function from inherited class when choosing base declaration for "Change signature"