TISTUD-5060 Add support to create github pull requests for current branch
  - first cut at getting something working.  ready to run in dev mode under debugger
Cleanup code and fix some bugs found while trying to use create PR command (talk about dogfooding!)
- Add "create pull request" entry in git menu.
- Add icon for create pull request command
- Add more specialized dialog for generating PR
Merge branch 'development' of github.com:aptana/studio3 into TISTUD-5060

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Merge branch 'development' of github.com:aptana/studio3 into TISTUD-5060
Update PR creation dialog to fix spacing issues, and pre-populate title/body (title with branch name, body with commit log since creation)
Remove unused dependency
use toast to display success
Address Michael's review comments:
  - fix to fire pull event when we pull
  - externalize UI strings
  - extract constants for strings (typically used in JSON)
Merge pull request #65 from sgtcoolguy/TISTUD-5060

TISTUD-5060 Add support to create github pull requests for current branch