Management of JRuby dependencies needs to be refactored out of JRubyExecUtils

[rtyler]

Right now there's some special behavior for managing JRuby dependencies, for example if you add a version prior to 1.7.20 we automatically add an updated jar-dependencies dependency.

This is now being used by base, jar and likely will be used by war too. It should be moved into a more general JRubyDependency class

[rtyler]

JRubyJar will no longer depend on this after #189