Add javadoc
Add response headers to BankResponse interface.
Add null check to DefaultBankResponse

* Add null check in constructor, throws IllegalArgumentException if input is null.
* Remove unnecessary null checks in methods.
Initial support for Google's coding conventions ( #10 ).

* Add checkstyle.xml
* Add eclipse formatter

Exceptions from http://google-styleguide.googlecode.com/svn/trunk/javaguide.html
* 120 characters is allowed per line instead of 100
* No reqirement of package-info.java
Rename BankDataProvider interface to Banking

Rename needed to be more descriptive.
Fix coding standard violations ( #10 )