Follow up to 82b4a53d29
On mobile, we just need to add `min-width: 0` to
`chat-live-pane` so it will not overflow the grid
defined in `main-chat-outlet.chat-view`.
The overflow could be triggered by:
1. Replying on mobile to a really long chat message
2. Uploading > 2 files
Both of these situations are fixed.
This css was causing the view on mobile to take more space than the available width. This was particularly visible with uploads due to a bug preventing the overflow, this is also fixed.
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**
