Modest improvements to Make a Move page.

* Some margin, padding, and rounded corner normalization.
* Adds WordPress "Add Media" button, since this is what we'll use for
adding media to move content.
* Use two-column layout, placing move metadata to the left and the list
of moves responding to on the right.
* Adds checkboxes for "responding to" moves. We'll certainly have a more
* elegant mechanism for de-selecting those, but underneath they'll be
checkboxes.