Install angular-ui-tree using bower
Add ui-tree to app dependencies, and load it in
Start work on reimplementing the topics sidebar using angular-ui-tree

Currently showing both versions of the topic tree, the one based on angular-bootstrap-nav-tree, and angular-ui-tree. The second of these is only partially functional at the moment (can select and reorder, but reordering does not actually save changes; can't add, rename, or delete yet)
Fix adding, renaming, and deleting topics using the new angular-ui-tree implementation