Add "git flow {bugfix,feature,hotfix,support} move/rename <name>" commands

[jkankiewicz]

Because there are no git flow {bugfix,feature,hotfix,support} move <name> or git flow {bugfix,feature,hotfix,support} rename <name> commands, one is forced to instead use the vanilla git branch -m <old-branch> <new-branch> command which won't update the moved/renamed branch's corresponding "[git flow ...]" section within the .git/config file.

This leads to problems like the following:

$ git branch -m feature/old feature/new
$ git flow feature start old
Fatal: Branch 'feature/old' already exists. Pick another name.

[jkankiewicz]

This is related to #407 in that there should be a corresponding git flow command for every vanilla git command that can potentially invalidate the "[git flow ...]" sections within the .git/config file.