1. `this.chat.activeChannel = null` was being done in twice
2. using `willTransition()` and checking transition.to.name prefix for route cleanup rather than using `deactivate()` was unnecessarily verbose and could be premature (if something aborted the transition you'd end up in a broken state)
3. `activeChannel` on Chat service can be null, check for that before accessing
Usage:
```javascript
api.addChatDrawerStateCallback(({ isDrawerActive, isDrawerExpanded }) => {
// do something
});
```
Note this commit also uses this new API to add a css class (chat-drawer-active) on the body when the drawer is active.
- better handling of drawer state using chat state manager
- removes various float and topic occurrences to use drawer
- ensures user can chat before doing a lot of chat setup
- fixes a bug which was creating presence errors in tests
- removes dead code
- Note this is also tweaking the UI a little bit as we are now using links/buttons in the header as needed
- It disables the find ideal channel in drawer mode, if loading `/chat` in drawer mode it will either reopen at the last position or just stay on index
