Don't report lints for data URIs

The `UrlQuotes` linter was incorrectly reporting data URIs as requiring
quotes. Add an exception to exclude these special URIs.

Change-Id: If4664e660e4ca81eba59d5b4f001c50975cf4e1b
Reviewed-on: http://gerrit.causes.com/43022
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>