[icos] Improve general appearance and add menu delay hover

[ahd44]

Various fixes and improvements to the appearance of the new theme.

• Improve consistency of width on some internal pages
• Add margin-top to admin tabs
• Disable toggling of menu open/close when not in mobile menu -- previously one could click on the menu headings and toggle the state of the mobile menu when in wide screen view, which is not ideal
• Re-enable box shadow on the dropdown menu
• Add menu hover delay and transition (new version of [icos] Add delay to menu hover and allow keyboard menu expansion #18)

[jonathanthiry]

Nice improvements! A couple of points:

• The menu animation still needs a bit of work when you go from hovering one item to another. At the moment it closes the dropdown completely and reopens it. It would look much better to have a smooth transition between both sizes.
• The admin tabs span the whole width, and it would be nice if they would be constrained to the content width.