Better handling big history by fetching changesets by lots

of 100 max (and creating commits in the same time)
before fetching another lot if needed....

& little refactoring
Merge pull request #626 from pmiossec/fetch_by_lots

[Need Tests] Fetch by lots
Merge back TfsHelper.PostVs2010.Common.cs in TfsHelper.Common.cs
Bring back all the TFS common code in TfsHelper.Common.cs (DRY!)
TfsPlugin is the same for all versions...
WrapperForWorkspace and WrapperForBranchObject could go in Wrappers.cs
Simplify a little more registry read for VS>=2012
Drop VsCommon in namespace

(because that's an internal namespace)
Merge pull request #629 from pmiossec/cleaning_after_vs2008_support_removed

Cleaning after vs2008 support removed
Update libgit2sharp to v0.18.1