more flexible ways to search repositories

1. For now the search box (the upper right corner one) only matches the repositories whose names start with the keyword, I suggest we should have it match any part of the repository name (like we do a full text indexing against the repository names?).

2. Should have a way to look up repositories by committer.

3. Repository grouping inside a given project.

The above suggested features are extremely useful when using Stash in a publisher-like firm which has tons of repositories in a single Stash server.