[ŧicket/11896] Set form_time with time() when marking all notifications read

form_time is only set if is passed via the form. Since the mark notifications
read link does not use the form, it will default to 0 causing the mark
notifications logic to only mark notifications read if their time is smaller
or equal to 0. This patch will change ucp_notifications to correctly set
form_time for the confirm_box.

PHPBB3-11896
[ticket/11896] Add ability to define expected message after posting

This change will add the ability to define the expected message after a
topic or post has been submitted with the methods create_post() and
create_topic(). If the expected message is not 'POST_STORED', we will not
try to get the topic and post id.

PHPBB3-11896
[ticket/11896] Add functional tests for marking all notifications read

PHPBB3-11896
[ticket/11896] Minor code improvements in phpbb_functional_test_case

Use assertContainsLang() and get rid of unnecessary logic in create_post()
and create_topic(). The docblocks were also slightly improved.

PHPBB3-11896
[ticket/11896] Correctly document return of null in docblocks

Also got rid of previous incorrect comment in docblocks.

PHPBB3-11896
[ticket/11896] Use $form_time and fix out of bounds $form_time

PHPBB3-11896
Merge remote-tracking branch 'Marc/ticket/11896' into develop

* Marc/ticket/11896:
  [ticket/11896] Use $form_time and fix out of bounds $form_time
  [ticket/11896] Correctly document return of null in docblocks
  [ticket/11896] Minor code improvements in phpbb_functional_test_case
  [ticket/11896] Add functional tests for marking all notifications read
  [ticket/11896] Add ability to define expected message after posting
  [ŧicket/11896] Set form_time with time() when marking all notifications read