Refactored out blueprints dependency from core module.

- Created dedicated blueprints module for blueprints graph base classes
- Reimplemented HeapGraphDatabase without dependency on blueprints
- Added HeapGraphDatabaseStressTest
Merge branch 'blueprints' of github.com:jdeolive/GeoGit into jdeolive-blueprints
Refactored out blueprints dependency from core module.

- Created dedicated blueprints module for blueprints graph base classes
- Reimplemented HeapGraphDatabase without dependency on blueprints
- Added HeapGraphDatabaseStressTest
Merge branch 'jdeolive-blueprints'
Add more information for geometry attributes in feature diff.
Added a way to see if a remote is reachable.  Updated push response.
Added time support for the web api log command.

There was an assumption that since and until were ObjectIds, so I added
new parameters for a date range.
Added web api commands to merge a feature and resolve a conflict using a specific feature.
Merge remote-tracking branch 'origin/pr/543'
Grammar
Space instead of backtick
Merge pull request #546 from tschaub/doc-typo

Minor doc typos
Attributes no longer look for hard coded values during merge feature.
Merge remote-tracking branch 'origin/pr/545'