Added font customization, arrow overlay, "ok" localization, overlay color customization

Sorry about the big update. We made some modifications for our use, and I wanted to make sure we synced up before we got too out of control. 

- Added an offset to view-based overlays, since they're normally centered and you might want to highlight another part of it.
- Ability to remove/hide sequences of views
- Tap/click anywhere to remove the overlay, not just the OK button
- Added listener so you can customize overlay behavior when an overlay is hidden.
- Added font typeface support, so you can change the title and description look a bit more
- Added an arrow pointer overlay... still need to test this a bit on my end and pretty up the different image resolutions.
- Added style entry for overlay background color.