Prepare Caava Helper to build admin UI Pages

Move all functions into classes CaavaCommon, CaavaHelper, and CaavaBugherd. Helper manages interface actions, Common is used for static calls, and Bugherd interacts with BH API.

# RoadMap

### Admin UI: Caava Tab
- [x] Add Caava Menu
- [ ] Add Social Subpage tab so clients can add authentication credentials via interface.
- [ ] Add Caava Design Company RSS Feed
- [ ] Add Bugherd Widget that displays Active bugs and status