Setting to skip relative paths fix on css minify

Sharepoint has virtual "/Layout" folder, so it makes sense to keep there
resources, which are directly "deployed" to the server.
Outside this folder can be development going on, e.g. css-files, which
eventually need to be compiled, minified and so on.
Having enabled css relative paths overwriting on minifying by default
without a setting to turn it off interfere with this folder structure.

Say we have
/Layout/Project1/Styles/fonts/font-awesome.woff
/Layout/Project1/Styles/css/plugins.css.bundle

now, bundle, references file:
/Styles/css/font-awesome.css

now replacing the "../font.woff" to "../../../../font.woff".

The commit is rather simple and merely adds a Misc option to css  bundle
compile check inside
WriteBundleFile,
controlling thus
CssUrlNormalizer.NormalizeUrls

Feel free to commit, or point out why that's unwise, how could we make
this better.
Merge pull request #245 from gr9zev/master

Setting to skip relative paths fix on css minify