* 3.1.x:
  [ticket/14855] Update notification and PM alert bubbles
  [ticket/14855] Update notification and PM alert bubbles
  [ticket/14855] Update notification and PM alert bubbles

Alternative implementation without removing notification from
the DOM, but changing the class.  So that style designers
might have more options (show/not show).
Fix tests better.

PHPBB3-14855

Alternative implementation without removing notification from
the DOM, but changing the class.  So that style designers
might have more options (show/not show).
Fix tests.

PHPBB3-14855

PHPBB3-14855

PHPBB3-14576

PHPBB3-11444

Currently the in-board method for the notifications is hardcoded and
cannot be disabled. This method should be in his own class extending
`phpbb\notification\method\method_interface`.

It also add the possibility, for each method, to be enabled by default (ie:
no entry in the DB => notification enabled).

https://tracker.phpbb.com/browse/PHPBB3-11444
https://tracker.phpbb.com/browse/PHPBB3-11967

PHPBB3-11444

We already use a token for preventing CSRF when marking notifications read.
Making a user confirm the marking read action serves no real purpose. No
information will be lost by just marking the notifications read but it will
prevent users from always having to confirm this action.

PHPBB3-13189

PHPBB3-12990