Add support for Karaf features in target platform definition file

[niport]

It might be useful to allow to add karaf feature support in target platform definition file. Two main reasons:

• Many OSGi-related projects provide a Karaf feature.xml, but not a p2 repo (for instance Apache Aries projects)
• The target definition file already allows to use Eclipse Feature (so it makes sense to integrate it with other feature formats).

The imported Karaf feature maybe can then be converted on the fly in an Eclipse feature, as it is already possible with maven artifacts.

[laeubi]

Karaf features can not be converted to eclipse-features per-se as they contain a lot of additional information that can be expressed as an eclipse-feature. Beside that, they technically can reference URL-Handlers that Eclipse do not understand (most notable wrap protocol).

Also one need to decide how they should be added, e.g. using an URL, should file local features be supported, what about referenced features and so on.

So I think this will be a lot of effort to have a generic support in PDE, but as feature.xml are often deployed as maven artifacts one might want to add support to the m2e-target to support transforming such a feature.xml into a set of bundles, this can work to some degree quite smoothly and m2e can also create a (new) pde-feature that includes bundles of a location.