Adjusted button and Edit Mode dropdown spacing. This makes sure that the buttons line up with the left hand side of the textarea, and that the Edit Mode dropdown naturally drops onto another line for mobile displays.
At @sunny's request, tweaked the position of the View Page button and Edit Mode dropdown so they fall in line with the button bar on mobile.

Also removed the editor's roundrect container - we don't really need to see it on mobile.
Moved search bar back into place.
Adjusted mobile styles for search pages.
Made history page nicer on mobile
Stop fieldsets from cutting off inputs on mobile
Merge branch 'feature-responsive-theme' into livepreview-maineditor-2