Currently, the comment dialog looks very squished when viewing it on mobile

with published comments. This change fixes this by stacking the published

comments box on top of the draft comment form, instead of side by side. We

now allow the dialog to be dragged from the "Other comments" header in

addition to the draft form header. It's more natural to try to drag the

top "Other comments" header on mobile when trying to move the dialog.
This also updates the z-index for the prev and next file attachment nav

buttons, so that it has a lower z-index than the comment dialog.

Tested the following on mobile and on desktop:

- Creating pure draft comments.

- Creating comments that are on the same region as an existing comment on

  an image.

- Creating comments that are on the same region as an existing comment on

  a diff.

- Creating comments that are on the same region as an existing comment on

  a markdown file.

- Clicking on an existing comment while not logged in.

- Moving and resizing the comment dialog.