FormCleanupRepository: rearrange GUI elements to better support filter by path
implemnent checkBoxPathFilter_CheckedChanged
GitCommandHelpers.CleanUpCmd: support path argument (and replaced Stringbuilder with simple +=)
FormCleanupRepository: implement optional path argument
Add "Clean working tree..." to context menu of FileTree tab
Merge remote-tracking branch 'gitextensions/master' into feature/clean_working_tree_with_paths

Conflicts:
	GitUI/CommandsDialogs/FormBrowse.cs
Merge branch 'master' into feature/clean_working_tree_with_paths
Merge pull request #1965 from feinstaub/feature/clean_working_tree_with_paths

Implement #1963: Clean working dir with optional path argument