Bug 887535 - Improve CSS and strings for l10n on privacy contact form

This makes the entire fields' labels localizable in https://www.mozilla.org/en-US/privacy/policies/firefox-os/ (I consider this as part of bug 887535).

Unfortunately this still doesn't solve the problem with placeholders defined in forms.py ('you@yourdomain.com' and ('Enter your comments...'), I tried putting those strings inside a _() but it won't work.

CSS changes:
* Remove width on h2 causing unnecessary wrapping in Contact us and Privacy policy title
* Header: set larger widht to fit longer localizations. Only downside of the larger width is that, at minimum width, the title is larger than the column for Spanish. en-US remains unaltered.
* Header: fix funny behavior between 1000px and 760px (en-US too).