Added ScopedTypeVariables extension

Changed eperiod function to be able take behavior as a argument,
so we can apply it over dynamicaly value.
Made truly adjustable 'period event'.

Thanks to guy from Haskell
subreddit(http://www.reddit.com/r/haskell/comments/1zvw4n/reactivebanana_how_to_implement_period_of_time/)
Merge branch 'feature-time-periods'