[ticket/12080] Add classes to color palette table to identify it more easily.

PHPBB3-12080
[ticket/12080] Reduce the palette options in all locations when responsive.

PHPBB3-12080
[ticket/12080] Stop responsive ACP sig textarea from dropping to second line.

PHPBB3-12080
Merge pull request #2037 from prototech/ticket/12080

[ticket/12080] Fix color palettes when responsive.