Clean-up trailing whitespaces

For the psychopath that lies deep down in each one of us.
Move Stage()/Unstage() tests to their own files
Update libgit2 binaries to 6950dca

https://github.com/libgit2/libgit2/compare/ad00376...6950dca
Remove orphan hack for Commits.QueryBy()
Restore support to filter since current orphan branch
Teach BranchUpdater to set merge branch directly
Stop sorting collections
Add SkippableTheoryAttribute
Add PathCase and related Repository members
Respect core.ignorecase in BuildRelativePathFrom()

Fixes #214
Add missing XML comment
Remove unused usings
Add Commit.DebuggerDisplay
Return Id for GitObject.ToString()
Move AheadBy/BehindBy into new TrackingDetails

Also removes common ancestor check for AheadBy/BehindBy to align with
git.git behavior. Fixes #301.
Remove sample hooks
Handle dot_git in DirectoryHelper
Add explicit cast from string to ObjectId
Update libgit2 binaries to 8cfd54f

https://github.com/libgit2/libgit2/compare/6950dca...8cfd54f
Add Stashes.Remove