deposit: display fixes

* Fixes the layout without touching the .container class
  from core Bootstrap and set proper breakpoint

* Adds new styles for the Instructions box

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
Ok, first point explains it. 

One more little thing to add - what do you think about putting this css inside a separated css file?