Move "Introduce..." classes to separate package
Rename Jet -> Kotlin
Move Maybe class and its inheritors to util package
Pseudocode: Track PSI elements which correspond to jump instructions
Drop ReturnInstruction
Fix bug in ShortenReferences visitor (do not skip PSI elements after modication)
Extract Function: Analysis and code generation
Extract Function: UI and refactoring handler
Use lazy analysis in JetNameValidatorImpl
Auto-generate test class for "Introduce variable" refactoring
Get rid of unnecessary write action
Generalize "Introduce variable" test
Translate AbstractJetExtractionTest to Kotlin
ExtractionTest: Change test data layout
Extract Function: Add test data
Fix incorrect diagnostic message for CONFLICTING_OVERLOADS

- the member and the container were mixed up
- don't output "defined in" part of the message, because we tell later where
  it's already defined in
- fix an instability of the diagnostic order in OverloadResolver by using
  LinkedHashSet
Render FQ name of default package as "root package" in OverloadResolver
Don't print descriptors' toString() in diagnostic messages

Use DescriptorRenderer.TEXT instead, it doesn't print the debug information
Refactor OverrideResolver and OverridingUtil

Fix warnings, simplify code. Untangle a very complex code related to
diagnostics on multiple default values and different names of parameters in
supertypes; fix a bug there, add test
Move some utilities from OverridingUtil to OverrideResolver

OverridingUtil will be present at runtime and we should strive to minimize the
size of our runtime classes

Also add a comment to getOverriddenDescriptors()
Minor, provide a nicer API in OverrideResolver for plugin