[IMP] mail, im_livechat: 'is typing...' indicator on mail channels

With this commit, most threads show an indicator when a member is typing
something. e.g.

	"Mitchell Stephens is typing..."

Supported threads:

	- DM
	- (public & private) channels
	- Livechat (Website & Backend)

Unsupported threads:

	- mailboxes (e.g. 'Inbox')
	- document thread (= 'Chatter')
	- support channel (with `im_support` module)

Some technical details:

	- This is a mix between 'start'/'stop' and 'regular notify' strategies.
	- On typing text in composer: notify 'start typing' to all members of
	  thread.
	- On clearing text in composer: notify 'stop typing' to all members of
	  thread.
	- A member can only notify once every 2.5 seconds to the server when he
	  starts or stops typing something (throttled, buffered notify call).
	- On receiving a message from someone that is typing: determine that he is
	  no longer typing.
	- On non-empty and unchanged composer text for 5.0 seconds: automatically
	  notifies all members of thread that he is no longer typing anything.
	  (This is like a 'soft / cooperative sender' timeout).
	- On non-receiving a typing notification of someone after 60 seconds:
	  determine that he is not longer typing something (This is like a
	  'hard / receiver assumption' timeout).
	- When some types for more than 50 seconds straight: notify that he is
	  still typing something (again and again every 50 seconds).
	- When two or more people are typing something (Multi-User channels), it
	  displays at most 2 typing users (ordering rule: longer typers first):

	  	"Mitchell Stephens, Marc Brown and more are typing..."

	- Timing summary:

		- Usually 2.5 seconds uncertainty.
    	- Up to 5.0 seconds uncertainty on typer inactivity.
    	- Up to 60 seconds uncertainty on typer page reload / browser tab
    	  closed / etc.

Future Improvements:

	- Detect page reload or browser tab close with loose of longpolling
	  connection

Task-ID 28188

0 files changed, 0 insertions, 0 deletions