Echo: Better support for non-default skins, as well as no Javascript

This provides some rudimentary styling support to make Echo usable
with the Modern skin.
It also fixes the Notifications special page so it is styled
correctly in Modern, CologneBlue, or with Javascript turned off.
Also some more tweaks for Monobook skin.
Retiring the 'feedback' link from the special page, per PM.

Bug: 47932
Change-Id: I633a93a78f5a78d0642a3a059fa6f7208f99cec4
Merge "Echo: Better support for non-default skins, as well as no Javascript"