Buildrequest data api implementation

Updates:
- Add buildrequest data api (including documentation, unit tests,
fakedb and fakedata)
- Change buildrequest db api 'mine' parameter to 'claimed_by_masterid'
- Minor fixes and factorization in FakeBuildRequestsComponent

Signed-off-by: Olivier Monnier <olivier.monnier@intel.com>
Data API: add filter options to buildrequest collection endpoints

Updates:
- adding filters to the BuildRequestsEndpoint.get() method
- replacing claimed='mine' option in buildrequest DB API, with
claimed=<master id>

Signed-off-by: Olivier Monnier <olivier.monnier@intel.com>
Merge branch 'buildrequest_data_api_doc' of https://github.com/omonnier/buildbot into events

Conflicts:
	master/buildbot/data/base.py