Fix broken zbar toolbar layout

This pull request will fix broken toolbar layout at ZBar Reader.
I have created `ReaderViewController` extends `ZBarReaderViewController` to fix some ZBar's issues.

This change:

* Overrides ZBarReaderViewController as ReaderViewController.
* Creates Custom Cancel Button with UIButton
* Improves toolbar height calculation
* Removes layoutReaderToolbar method
* Fixes Memory-Leak at ZBar Reader View creation