Made draft RegionCommentBlock movable, by drag-and-drop.
Currently, a RegionCommentBlock is not movable, even if it is a draft. This change makes draft RegionCommentBlocks movable by drag-and-drop. Users finish moving it by mouse-up action, and the draft RegionCommentBlock's new position is saved on server.

Passed all tests in "/js-test/".
Browser test done:

  1. Go to file attachment review page, for example, http://localhost:8080/r/7/file/4/

  2. Make draft comment

  3. Try moving

  4. Refresh the page

  5. See if the bounds are updated
Edge cases tested:

  1. Open file attachment review page, make move "once" and refresh. => Working well. Confirmed the location is updated.

  2. Try click-and-drag non-draft commentBlocks. => Non-draft commentBlcoks are not movable. Working as expected.