Added HasFormValue and HasValue<Boolean> implementations to CheckBox and CheckableInputButton
Added JSNI methods to Input to get/set value
Revert "Added HasFormValue and HasValue<Boolean> implementations to CheckBox and CheckableInputButton"

This reverts commit abc3a09cc096c485ea531719e19948e110d14740.
Fixes for issues #27 & #29
Merge pull request #31 from gslender/master

Fixes for issues #27 & #29 (try #2)