[ticket/12612] Move functions from posting.php to functions_posting.php

PHPBB3-12612
[ticket/12612] Move functions from memberlist.php to functions_display.php

PHPBB3-12612
[ticket/12612] Move function from ucp.php to functions_user.php

PHPBB3-12612
[ticket/12612] Move functions from mcp.php to functions_mcp.php

PHPBB3-12612
Merge remote-tracking branch 'github-nickvergessen/ticket/12612-ascraeus' into develop-ascraeus

* github-nickvergessen/ticket/12612-ascraeus:
  [ticket/12612] Move functions from mcp.php to functions_mcp.php
  [ticket/12612] Move function from ucp.php to functions_user.php
  [ticket/12612] Move functions from memberlist.php to functions_display.php
  [ticket/12612] Move functions from posting.php to functions_posting.php