Squashed implementation of native git support

Initial Commit with changes from https://github.com/ktoso/maven-git-commit-id-plugin/pull/93/

Added some tests which modify the abbrev length of the git.discribe to identify problems with the native git thingy

Added some tests which modify the abbrev length of the property git.commit.id.abbrev to identify problems with the native git thingy

Added some integration-tests for native git config tests

Added a new layer for git-Runtime (native VS jgit)

Improved the new Git-Dataprovider-Interface which now will handle the filling of the main git properties

changing the native git implementation to native git calls, so no xml or json parsing is necessary
test fixes
Merge pull request #120 from ktoso/native-git

Native git