Add more configuration for how links are opened

These are some configuration points I've added to the apps I've built with Lavaca. 
Thinking they might be useful for others as well.

- Cordova got it built-in that target="_system" will open with the system
  browser, meaning that it can open a link with any other application
  installed if it's registered for that handler. Or just opening
  mobile Safari or the Android Browser if needed.

- rel="force-back" follows the link normally but animates it with the
  back animation.