Added disk quota support, removed memory quota validation.

Java API changes
* Added `updateApplicationDisk` to complement `disk` parameter of `createApplication`.
* Added tests for validating disk quota on app create and update. 
* Removed `getApplicationMemoryChoices` method since memory quotas are no longer constrained to a fixed set of options. 

Maven and Gradle plugin changes
* Added the ability to specify disk quota in plugin configuration. 
* Removed validation of memory quota.
* Removed defaulting of memory quota since a default is now configured in the CF deployment. 
* Updated output of "cf:app" and "cf:apps" Maven goals and "cf-app" and "cf-apps" Gradle tasks to include disk usage and quota, and to more closely match evolving `cf` CLI output.