Extractor refactoring - ability to use static fields/methods

[EvSpirit]

Working further on #300

I've done a bit of refactoring to solve a couple of issues:

• Impossible to use static fields/methods (e.g. String.valueOf() or Integer.MAX_VALUE)
• Incorrect method selection - parameter classes/types are not validated (e.g. String.valueOf(double) and String.valueOf(int) give different values)

So a bit of refactoring and everything is fine.

• ReflectionUtils replaced with common-lang3 MethodUtils/FieldUtils (to keep parameter types validation clear)
• Callable list removed - try get result at each step to optimize things a bit

I'll close #300 as that PR solves previous issue.

Thanks in advance ;)

[coveralls]

Coverage decreased (-0.07%) to 93.04% when pulling da6a40a on EvSpirit:extractor into fad5332 on jtwig:master.