Windup processor windup 253 rebase

Rebase of https://github.com/windup/windup/pull/228/commits 

    WINDUP-272 Refactor GraphContextFactoryImpl and GraphContextImpl
    WINDUP-253 Refactor WindupProcessor/Impl
    WINDUP-254 Improve error message in RuleSubset.
I agree with Jess that this should be replaced with a context.init() call with 0 parameters.