Add font weight and italic options for brand font

Lets you choose from some of the other weights of font available,
and turn italics on and off.

Ideally you should only do this if the font actually has these
weights and italics, or you might end up with the page default
font, or an artifically slanted or bolded version.

Note that due to the way Google Fonts names these fonts they can
clash with the other weights of the same font imported separately
e.g. if you import a very heavy weight of Open Sans or Lato which
you also use in the rest of the page, you might see certain letters
(those used in your site shortname) using the heavier weights.

One of my favourites so far is Open Sans, italic, at 800 weight.
And a 0.2 alpha drop shadow added via the CSS comment box seems
to help too.
Merge pull request #227 from ds125v/brand_font_italicbold

Add font weight and italic options for brand font