Added options to dismiss on inner tap dimiss on passthrough tap

Use dismissOnTap and dimissOnPassthroughViewTap BOOL properties
Added ^dismissCompletionBlock(WYPopoverController *dimissedController) property

Can be used in addition, or in place of, the delegate's popoverControllerDidDismissPopover: method.
Merge pull request #27 from obviousengineering/oe-improvements

Improvements: dismissOnTap and dimissOnPassthroughViewTap properties; optional dismissCompletionBlock