Branch Searching in Branch Dropdowns

It's unclear just how many branches we will have, but if it gets beyond a small number, sorting through them will be messy. The dropdowns throughout the interface only show unmerged branches (which is good). However, you should still be able to access an unmerged branch without having to hard-code the URL.

There should be a text box at the beginning of the branch dropdowns that lets you filter **all** branches by name, including merged branches. This would be similar to how test case dropdowns let you filter by name by typing.