Add option to skip maven-* properties when generating a p2 repo

[cdietrich]

As a tycho user i'd like to have an option to skip maven-* properties when generating a p2 repo

[mickaelistria]

What problem would that fix; or what extra value would that provide?

[laeubi]

Issue is described here:

• Milestone does not build on Jenkins eclipse/xtext-eclipse#1931

and most likely this is better fixed with this:

• Remove the mapping of maven artifacts at the injection-phase #1664

than trying to mangle any configuration options into the generation part itself.

[laeubi]

I think the solution is not to skip these properties but having finer control on how injection of maven model works.