fix($state): use $browser.baseHref() when generating urls with .href()

If an angular app is placed in a subdirectory and a <base href="..." /> tag is used, ui-router should use the configured value when generating urls through $state.href(). Thanks to @mfield for the testing help!
Merge pull request #528 from tgecho/basehref

Prepend the baseHref to $state.href() generated urls if it exists.