A fairly significant refactor to support the idea of polyfill 'variants' (see #59).

The interleaving of resolving dependencies and choosing the correct variant for the UA was a major headache and cost me most of the afternoon, and I'm not totally happy with the result.  The difficulty is that each variant may have different dependencies, so you can't resolve dependencies until you've selected a variant.  The two therefore have to alternate as we descend the dependency tree.
Update tests.
Fix bad rebase
Remove errant console.log
Fix a couple of bugs left over from rebase
Improved director
Add a token test so that all test suites emit the 'end' event even if there aren't actually any tests configured.
If the director is used with 'configuredonly' then only polyfills configured for that browser are tested, additionally, qs parameters from the director are passed to each loaded iframe
Update to use new director URLs
Updated shrinkwrap
Updating saucelabs task, refresh immediately to save some time.  We need to still refresh as iOS simulator seems to need a kick still
Update configs for matches, mutation and placeholder
Variant syntax for defineProperty
Variant syntax for getOwnPropertyNames
Variant syntax for Window
Variant syntax for Window.polyfill
Improve attribution metadata
Variant syntax for devicePixelRatio
Variant syntax for getComputedStyle
Variant syntax for localStorage