Add column blocks to internal pages

[knice]

User has requested the ability to add column blocks to internal pages. There are several considerations:

1. There are currently two ways to assign blocks to column regions: dept_column_* and three_column_*.
   • Which one should get implemented? 👍
   • Or both?
   • Or create new regions and make them show up only on internal pages. 👎
2. What if only one or two blocks are assigned to the 3 regions?
   • Do whatever is done on the home pages?
   • Don't render any blocks unless there are three assigned to the 3 regions? 👎
   • Use flex layout to dynamically adjust width. 👍
3. The area for column blocks is more narrow on internal pages.
   • Limit internal page block placement to two blocks maximum? 👍
   • Design a new look for internal page blocks? 👎