Merge pull request #137 from sbesson/admin_tools

Admin tools
Modify the default exclude parameters for all merge commands

- Set ['exclude', 'breaking'] as the default exclude labels/comments
- Teach find_candidates() to parse comments for any exclude label
- Allow find_candidates() to include PR using either PR attributes or include
  comments (for any include label)
- Fix filter unit tests
Add test case for PR inclusion via comments
Fix conflicting message typo
merge master -D org -I include -E exclude: PR 138 (Modify the default exclude parameters for all merge commands)
merge master -D org -I include -E exclude: PR 139 (Fix conflicting message typo)