talkback: fix line breaks before all messages
warn: attempt to fix loss of optional message for some admins

Even though the element containing #block_reason is removed from the
form, the |block_reason| property of the form is still accessible.
Doesn't make sense, and hopefully this fixes it.
tag: amend description of {{dead end}} to its actual meaning

Per request at WT:TW
warn: fix label for {{uw-bite}}

Per request at WT:TW.
Update modules/twinklewarn.js

Removed a deleted warning template.
warn: add red notice to show correct use of {{uw-username}}

Per discussion at WT:TW and WT:UAA.
warn: correct placement of red notice div in DOM
morebits.css: small tweak to QuickForm header selector

This is needed for upcoming changes I plan to make. It works in IE9 and
latest Firefox, and as such it probably (!) works in Chrome.