Support Mercurial Subrepositories

Currently Mercurial subrepositories aren't visible in the SmartGit gui.

Changes to the sub repository related files (.hgsub and .hgsubstate) are visible but there is no way of seeing the contents of the sub repository itself.

If you have a repository layout like below:

• main-repo
  • sub-repo (points to ..\sub-repo)
• sub-repo

When viewing main-repo in SmartGit I would expect to be able to also browse the nest sub-repo folder but it is missing from the UI.

There are also no commands for pulling and updating subrepositories.