Group and Columns blocks: move color controls to toolbar

[ZebulanStanphill]

When choosing where to put block controls, the most important ones should be placed either within the block itself (e.g. the caption field of an Image block) or in the toolbar (heading level of a Heading block). Right now, the Group block puts its background and text color controls in the inspector. I think they should be moved to the toolbar for the following reasons:

• One of the main reasons to use a Group block is to provide a common background color or text color to a group of blocks. This important feature should not be hidden away in the inspector, which is supposed to be reserved for advanced controls.
• The Group block toolbar is currently very small, so there's more than enough room to put the controls.
• Putting the color controls in the toolbar makes them more visible and quicker to access.
• The Navigation block already does this, so there is a precedent in core blocks.

Similar arguments could be made for the Columns block, which recently got background and text color options as well.

[paaljoachim]

Thanks for bringing this up Zebulan!