Eliminate extended mode, and other modes clean-up

- Merge LanguageMode and StrictModeFlag enums
- Make harmony-scoping depend only on strict mode
- Free some bits on the way
- Plus additional clean-up and renaming

R=ulan@chromium.org
BUG=

Review URL: https://codereview.chromium.org/181543002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19800 ce2b1a6d-e550-0410-aec6-3dcde31c8c00