Changes to allow converting things from the ESP TFS repo.

Allow mapping domain users (from old domains, non-existing users, etc)
Added settings to "un-hard-code" project-collections /roots etc. from the source.
Added OutFile option to allow easier debugging, printing progress to the console while running, without having to pipe it into git fast-import.
Added SkipCommits setting to allow ignoring certain commits (typically problematic commits - unavailable project/collection for instance).
Shoe proper progress during operation.