Entity Redesign

Removes all current models and replaces them with entities. Currently,
only AbstractDataEntity and AbstractDataEntityCollection are really
fleshed out. Boardgame, Name, and Version are just object stubs for
now.

Adds an inflector to help with camelcaseing and underscoring strings as
needed by the AbstractDataEntity class.

Adds basic unit tests for AbstractDataEntity classes and the Inflector
class.

Adds phpunit to composer and adds a phpunit.xml.dist file along with
a test bootstrap autoloader.