Add additional information to exceptions

I have added constraints for each exception that specify the exact cause and allow additional information.

I have added a Gradle file to support the use with Android Studio. 
Furthermore I have added an IbanChecker that validates incomplete IBANs. 
The Android code has moved to my iban4android project. 
'mvn package' still works, but please check if the change of the test cases are okay. I have moved some error cases to the UnsupportedCountryException and replaced the InvalidateArgumentException with their corresponding exception.