Git.hub and NBug added as submodules

Cherry-picked from: 2702989d6dad2d9b4950511d77b3c48796a3ef94

Conflicts:
	GitExtensions.VS2010.sln
	GitExtensions.VS2012.sln
	GitExtensions/GitExtensions.csproj
	GitExtensions/packages.config
	TranslationApp/TranslationApp.csproj
Use read-only urls for submoduls.
Changed location of Git.hub.dll in post build event
Check for updates using GitHub api. There is a bug in WebClient that causes AV. Closes #2006.
Added IconFileStatusUnknown - when git exits with error then GitExt crashes with IndexOutOfBounds