To reduce risk of conflict renamed action to actionBlock

To address the [comment on commit `e2c23df0708c7afb6a824d26d433a447c89dda30`](https://github.com/jivadevoe/UIAlertView-Blocks/commit/e2c23df0708c7afb6a824d26d433a447c89dda30#commitcomment-3440433) by @MrNickBarker I propose renaming `action` to `actionBlock` in `RIButtonItem`. 

I'm also including an example projet to make testing UIAlertView-Blocks easier.