Unified common classes and interfaces. Closes #1, closes #3.

* Add root class JCaching.
* Add factory class for backend implementations.
* Change position for SocketMemoryBackend root class implementation.
* Add factory class for protocol implementations.
* Add Apache CommonsConfiguration library to handle properties parametrization.
* Add Apache CommonsLang library.
* Change CacheDeamon from static methods to instance methods.
* Change test unit implementation for SocketMemoryBackend to instantiate a threaded server only once.
* Add default properties configuration file.
* Change example to use the library more verbosely.
* Add javadoc comments + TODO entries.
* Add diagrams in /docs + class diagram image.
Merge branch 'common-interfaces'