Extract single point of entry for all change signature refactorings and fixes (remove parameter, add parameter)
Change signature now affects overriding functions as well
Ask 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
Dmitry Jemerov