Removed jgit dependency.

Removed jgit dependency and added dependencies to
git plugin and git-client plugin.

Unless a classloader which loads the plugin's classes first is used, the jgit jar will be provided from
the git or git-client plugin, since they are loaded first. By removing the dependency to jgit, this is more clear and developers are not tricked into thinking that the version of jgit is static. In my case, older git and git-client plugins provided jgit 2.2 which caused weird bugs.