The settings tab of each category channel should now present the option to allow or disallow channel wide mentions: @here and @all.
When disallowed, using these mentions in the channel should have no effect.
- 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
Toggling channel settings shows a status message when saved. This status message is not accessible to screen readers. This commit ensures that the status message is made accessible.
