git: Initial implementation of git clone dialog

Adds a git clone dialog for "out-of-version-control" actions, consists from a clone dialog itself and a clone progress dialog.

Progress dialog is at fileviewgitplugin.cpp for code review simplification. There is progress dialog already in svn plugin which we could use, but this leads to a project structure change, so it should be done separate.

Clone dialog has the most common day-to-day options and inspired by TortoiseGit clone dialog.