[WIP] Angular-ify the Dictionary tree & editor

> *WORK IN PROGRESS*

Started work on migrating the legacy Dictionary tree and editor over to Angular.

I have opened this pull-request to start a dialogue with the core team about its development and progress.

*Task list:*

* [x] *Tree* - Web API controller
* [x] *Tree* - Angular resources
* [x] *Tree* - Depreciate legacy tree
* [ ] *Editor* - List view (Angular template + controller)
* [ ] *Editor* - Edit view (Angular template + controller)
* [ ] *Editor* - Model mapping (AutoMapper configuration)