Unify query_form structure on calendar/gantt views (#26125).

Unify query_form structure on calendar/gantt views (#26125).

This:
* moves the p with inline style on the calendar view (which
  wraps the navigation buttons) out of div#query_form_content
  and adds the contextual class to the element to unify this
  with the gantt view (and to remove the inline style from
  the element now that it's styled through a stylesheets'
  style [.contextual in fact]);
* restores the 12px font-size of the calendar navigation
  buttons;
* increases the font-size of the gantt zoom buttons to 12px;
* increases the margin of the calendar navigation and gantt
  zoom buttons to 12px 0px.

Patch by Mischa The Evil.

git-svn-id: http://svn.redmine.org/redmine/trunk@16703 e93f8b46-1217-0410-a6f0-8f06a7374b81