2757 Disable chapter, comment, and new work submit buttons once clicked

Once clicked, submit/post buttons on comments, chapters, and new works (and chapter or new work preview pages) should switch to "Please wait...". `:disable_with` applies the `data-disable-with` attribute to the buttons and rails.js takes care of the text change.

http://code.google.com/p/otwarchive/issues/detail?id=2757

Updated from https://github.com/otwcode/otwarchive/pull/771