[ticket/12559] Add forum setting to limit subforum legend

Squashed all commits, they were basically just typos and errors

PHPBB3-12559
[ticket/12559] Applied DeMorgan and removed unnecessary true:false

PHPBB3-12559
[ticket/12408] Add quick setting for "default guest style" to ACP

PHPBB3-12408
[ticket/12408] Simplified queries

PHPBB3-12408
[ticket/12408] Code cleanup

Rebased to see if travis will finally play along

PHPBB3-12408
[ticket/12408] Public functions and updated doc block

PHPBB3-12408
[ticket/12408] Changed lang vars, added fieldset and removed "default"

PHPBB3-12408
[ticket/12559] Updated copyright information

PHPBB3-12559
[ticket/10472] Fix ACP overflow:hidden problem for medium-sized screens

PHPBB3-10472
[ticket/10472] More clearing and white-space fixes

PHPBB3-10472
[ticket/10472] Fix weird padding on input type=number

PHPBB3-10472
[ticket/12535] Make <a> adjust to the image width

PHPBB3-12535
[ticket/12535] Add events to subsilver2

Forgot subsilver... yet again

PHPBB3-12535
[ticket/12598] Improve search box styling

PHPBB3-12598
[ticket/12649] Change display-options and sorting to dropdown

PHPBB3-12649
[ticket/12649] Add the sort icon CSS

PHPBB3-12649
[ticket/12649] Move <form> element to original template

PHPBB3-12649
[ticket/12649] RTL alignment fix

PHPBB3-12649
[ticket/12649] Use new sort options title attribute

PHPBB3-12649
[ticket/12649] Remove last old clear-div

PHPBB3-12649