Allow creating Derby as a JNDI datasource

[bindul]

The goal for this issue is to be able to set up and run tests looking up data sources from a JNDI lookup (as in an application server or servlet container); without requiring full blown application server (or servlet container) running.

This one builds on (hence, depends on) #24

• Define optional JNDI context initialization mechanism
• Provide implementation for using Tomcat Naming context (with Tomcat as an optional dependency)
• Extend the configuration to be able to define Context Initialization mechanism or none (context initialized outside)
• Allow creation of a JNDI datasoure; which should be able to use any context provided (our sample one; or a standard app server one).
• Unit test to use Tomcat context initialized through above, or outside
  • In Memory
  • Directory
  • Jar
  • Classpath
• Extend the datasource documentation to talk about all of the above