conversation: improve typers management

Now, a client should not do any logic and not store preferences
client side.
+ When a member is removed while banned, the typing indication
is updated
+ Timeout is computed both for sender and receiver
+ Sending and receiving a composing status is managed by the
account's config.

GitLab: #951
Change-Id: Iba9441736eec4f71695bfbd609d4b9e8b6adcb73