Adds a “Color” setting to entry types.

When an entry type has a color selected, entries of that type will be filled in with that color within cards, chips, and inline-editable Matrix blocks.

Matrix fields set to the “inline-editable blocks” view mode have also been redesigned a bit:

• The titlebar now includes the entry type icon, if it has one
• Matrix blocks with only one entry type no longer show the entry type icon/label in their titlebars.
• Block bodies now have a white background color, to improve the visibility of nested chips/cards/Matrix blocks.
• The “Add” button is now always displayed as a menu, unless there’s only one block type. No more button group listing all types. (This way it’s always consistent regardless of viewport size, and so we can show the block type icons, which would have looked awkward in button group form.)