Squashed commit of the following:
Basic Revision history implementation, including DVCScommit class and interface implementation for Git. It works correctly with simple revision history (actually it works fine with all things could be done with DVCS in KDevelop). Simple history with merges is ok too. Some API documentation (essential). Branching tests for GitExecutor (but can be used in all executors). Few Easter Eggs for translators :) Fixes for Git to allow CommitManager to work correctly with "no commits" repos. Some minor fixes/changes.