This commit changes the ChatThreadsManager into a native
class instead of an ember service, and initializes it
for every ChatChannel model. This way each channel has its
own thread manager and cache that we can load/unload as
needed, and we also move activeThread to the channel since
it makes more sense to keep it there, not inside the chat service.
The pattern of calling setOwner with the passed in owner
from ChatChannel is adapted from the latest ember docs,
and is needed to avoid the error below when calling services
from the native class:
> Attempting to lookup an injected property on an object without a container, ensure that the object was instantiated via a container
It works well _only_ if we use our own getOwner wrapper
from addon/lib/get-owner, which is for backwards compat.
c.f. https://guides.emberjs.com/release/in-depth-topics/native-classes-in-depth/
This commit introduces the skeleton of the chat thread UI. The
structure of the components looks like this. Its done this way
so the side panel can be used for other things as well if we wish,
not just for threads:
```
.main-chat-outlet
<ChatLivePane />
<ChatSidePanel>
<-- rendered with {{outlet}} -->
<ChatThread />
</ChatSidePanel>
```
Later on the `ChatThreadList` will be rendered here as well.
Now, when you go to a channel you can open a thread by clicking
on either the Open Thread message action button or by clicking on
the reply indicator. This will take you to a route like `chat/c/:slug/:channelId/t/:threadId`.
This works on mobile as well.
This commit includes basic serializers and routes for threads,
as well as a new `ChatThreadsManager` service in JS that caches
threads for a channel the same way the channel threads manager does.
The chat messages inside the thread are intentionally left out
until a later PR.
**NOTE: These changes are gated behind the site setting enable_experimental_chat_threaded_discussions
and the threading_enabled boolean on a ChatChannel**
