Removal of old files and update of assets and imports

Joint work with aab

Read more / less feature is back (and probably ugly). It has probably been
removed when refactoring the old chatter.

[FIX] tools: html shortening: encoding issue

UP and DOWN (keydown event) move the cursor position at begining and end of the input text value. ENTER keypress event add 1 to the cursor position. So these events are now 'preventDefault'.

- In the chat, when loading more messages, automatically scroll to the previous
oldest message instead of staying at the top;
- In the chat, don't use the event 'scrollTop < 50' to load more messages as
it won't work on mobile (all the webclient is scrolling, so the client action's
scrollTop will always be 0);
- Generalize the way to load more messages between chat and chatter by moving
the logic to the MailThreadMixin and creating a common template;
- Improve the style of this 'load more messages' button

mail_channel: call create with mail_create_nosubscribe=True to not subrscribe creator as follower,
since channel is not a mail thread (channel followers make no sense)

mail : adaptation with new chm controller for attachment, and remove author_ avatar from message format

deprecated since 6baf611df1064a3ae5f6368d3a35b3c3d7779543

Also fix path do mimetypes, now located in web.

- DOM simplification
- LESS refactoring
- Unused code removal
- Integration in new design
- Fix a bug when trying to scroll the the last seen message in an empty channel
 (bug was due to the assumption that an empty jQuery element equals false,
 which is wrong)

remove unused imports, add missing semicolons, ...