Update solution to Visual Studio 2013

Update LibGit2Sharp to 0.17
Remove unused reference
Update LibGit2Sharp nuget
Migrating MSBuild-Integrated solutions to use Automatic Package Restore
Rename user control
Extract base class DiffMarginBase
Encapsulate margin core functionalities in MarginCore
Introduce interface IMarginCore
Refactoring to avoid to some View to ViewModels
Move some more responsibilities to MarginCore
Renaming refactgoring
Move the way to calculate diff position to the margin
First working solution with VS 2013 Enhanced Scrollbar
Minor ui fine tuning
Update version to 1.3.9, pre-release of 1.4.0
Remove code duplication
Minor code cleanup
Fix crash deleting changed lines at the end of a file (close #30)
Update version to 1.3.9.1, pre-release of 1.4.0
Replace Button by Control in Scroll margin view