* Extract GitLogSingleCommitAction - the common class
for all Git actions on the log, which operate on a single commit.
* Implement "New Branch" and "New Tag" actions. Use GitBrancher for
the first, reuse the existing CreateNewTag for the latter.
* Regroup actions in plugin.xml so that they form a single group which
is then added to the Vcs group.
It lets add a separator, and also makes the code more clear.
Kirill Likhodedov
32c3c35969