[ticket/13125] $user->browser to $browser

PHPBB3-13125
[ticket/13033] Fix "Duplicate entry 'notification.type.*' for key 'type'"

Caused by the solution of PHPBB3-12990

PHPBB3-13033
Merge pull request #3018 from Senky/ticket/13125

[ticket/13125] Uploaded avatars are not displayed

* Senky/ticket/13125:
  [ticket/13125] $user->browser to $browser
[ticket/12368] Always clean the cache prior to run the migrations

PHPBB3-12368
Merge pull request #3022 from Nicofuma/ticket/12368

[ticket/12368] Always clean the cache prior to run the migrations
Merge pull request #3017 from nickvergessen/ticket/13033

[ticket/13033] Fix "Duplicate entry 'notification.type.*' for key 'type'"
[ticket/13134] Add core event to the root of the function display_forums()

PHPBB3-13134
Merge pull request #3025 from rxu/ticket/13134

[ticket/13134] Add core event to the root of the function display_forums()