p2asmaven convert p2 transitives into maven transitives

[nedtwigg]

@akhikhl's Unpuzzle uses OSGi Require-Bundle information to create maven dependencies. @stempler created a fork of Unpuzzle which also handles Import-Package/Export-Package to create maven dependencies. It would be awesome if Goomph could do something like this:

p2AsMaven {
    group 'p2', {
        repoEclipse '4.6.0'
        iu 'org.eclipse.jdt.core'
        transitives 'requirebundle`, `importpackage`
    }
}

Stuff required to make this work

• [ ] Extend MavenRepoBuilder to support the various strategies.
• [ ] Extend AsMavenGroup to allow the DSL for specifying strategies for determining transitive dependencies.

I don't have time to build this right now, but if anyone else builds it I'd be happy to merge. If you want this feature, +1 this issue. If you want to tinker with building this feature, let us know here and I'd be happy to help.