State now stores individual app definition versions instead of appRepositories per app
Minor cleanup.

- Removed unused class `History` and associated tests.
- Added docblock comments to `AppRepository`.
- Various minor formatting fixes.
Merge pull request #187 from rbpark/master

State now stores individual app definition versions instead of appRepositories per app
Merge pull request #192 from mesosphere/rbpark-master

Minor cleanup.
AppRepository.expunge now deletes current version

Fixes #194
Removed duplicate code and tests: ConstraintModule
AppDefinition validator now respects random ports

Renamed the validators used to reflect the more specific behavior they now implement.  Includes a new test in AppDefinitionTest.
Replace contributors with authors section in README

Rationale:

* Git already tracks this information
* GitHub has a "Contributors" tab that gives statistics based on Git
  history
* The section adds little value to consumers of the document
* A static list is difficult to maintain, which is why it historically
  has been out of date

Fixes #193.
Merge pull request #196 from mesosphere/validation-respects-random-ports

AppDefinition validator now respects random ports
Merge pull request #197 from mesosphere/contributors-to-authors

Replace contributors with authors section in README
Better handling of invalid requests
Replace deprecated launchTasks() call
Send only editable attributes when updating an App

Backbone sends all model attributes by default when a model is saved. In
an App's case, that includes immutable values like "tasksRunning" and
"tasksStaged" and the "version" value, which prevents any change from
happening.

Add a "editable attributes" list that is a whitelist of attributes that
should be sent to the server on save.

Fixes #198.
Merge pull request #201 from mesosphere/parse-exceptions

Better handling of invalid requests
Add description of overriden save method
Include CPUs in editable attributes
Merge pull request #202 from mesosphere/editable-attributes-whitelist

Send only editable attributes when updating an App
Fix #200 Add version to tasks
Merge pull request #207 from BenWhitehead/bug-200

Fix #200 Add version to tasks
Added jackson-case-class-module to the build.