Refactor ninja-core

[raphaelbauer]

Complexity: Large

May be divided into different tasks.

• make freemaker separate module
• make jpa separate module
• Make it backwards compatible. Maybe we need a new ninja-core that acts as bom. Then a new ninja-atomic that is the new ninja-core. Not sure. ninja-classic sounds cool as well. Maybe we don’t need to be backwards compatible.
• Make ninja-core much lighter and require minimal dependencies. Create a new "ninja-classic" module that lets you quickly pull all the standard stuff back in.
• Migrate ehcache, memcached, freemarker, jackson-json, jackson-xml, flyway out of ninja-core and into their own separate maven modules that line up with those dependencies. E.g. ninja-freemarker, ninja-jackson-json, ninja-memcached, etc.
• Users would simply switch depending on ninja-core to ninja-classic if they want to quickly upgrade. Untangling the unit tests for these make each migration not as straight forward as you'd think. Perhaps an issue for each dependency we migrate. The big ones are ehcache and jpa/hibernate.