Fix: Adjust block container only when containing a block with a column class (fix #597)

[swashbuck]

Fix #597

Fix

• Adjust block container only when containing a block with a column class. Adding a column class to a component alone should not affect the block container width.

Testing (use case 1)

Test using column classes on components.

1. Create a block with a single width Text and Graphic component.
2. Add bg-color black to the block
3. Add col-md-4 to the Graphic component

Expected results

The black block background should continue to span 100% of the page width.

Testing (use case 2)

Test that the new block column classes still work as expected.

1. Add col-md-8 to a block
2. Add bg-color black to the block

Expected results

Block container should be content width rather than full page width. The actual block itself should be 8 columns wide.

[kirsty-hames]

Good spot @swashbuck! Apologies I missed this with the initial PR. This now works as expected 👍