Investigate moving main form action buttons to sidebar

Problem/Motivation

Now when #2897504: Node edit form metadata form items could go to the right is in we could investigate an option to move main form elements to the sidebar and keep sidebar on the screen while scrolling.

Proposed resolution

• The whole right sidebar on node edit form should stay on the screen while the editor is scrolling node form. Bootstrap already use some libraries for this (http://tether.io/), investigate that approach first.
• Move action form buttons to the right and put it on the bottom.
• We should have enable/disable theme config option for this. Possibly we need two config options one for scrolling and another one for moving the buttons.
• The whole thing could look like this:
  

Remaining tasks

Lets figure first is this is a good idea and then implement if it is. There are a couple of separate sub issues here, maybe create follow ups if needed.