[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
[ticket/12649] Move "only topic" (MCP) back to in-line

PHPBB3-12649
Merge remote-tracking branch 'origin/ticket/12649' into test/all

Conflicts:
	phpBB/styles/prosilver/theme/buttons.css
	phpBB/styles/prosilver/theme/images/icons_button.png