General cleanup of some types in the Stripe Java bindings.

Refactorings of these varieties:

* No need to cast null
* Cleanup imports
* Made some objects final
* Don't set to null when it's null by default
* Fix indentation in some places
* No longer create a Double allow implicit casting int->double->Double
Make travis execute maven in a non-quiet manner

When the build breaks in maven, it's useful to go through logs to
determine what broke. This commit turns off `--quiet` so the logs
aren't supressed.
Lock versions of plugins.

This is especially important because maven-javadoc-plugin v2.10
is a version that has breaking changes.

http://jira.codehaus.org/browse/MJAVADOC-408
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