Maven plug-in with example recipe for producing high quality bundles.

This commit adds a Maven plug-in for generating OSGi bundles based on
Maven artifacts. It also adds a basic structure and an example recipe.

How the Maven plug-in works:

 1. Direct dependencies are collected an unzipped.
 2. Direct dependencies are then merged with the output produced
    already by the Maven module, i.e. any content in src/main/resources
    or even source code compiled before from src/main/java will take
    precedence over stuff coming from dependencies.
 3. OSGi manifest is generated (via Apache Felix Maven Bundle plug-in).
      - Bundle-SymbolicName is assumed to be the artifact id
        (This is an important assumption made throughout the plug-in
        which can't be changed!)
      - Instructions for BND can be specified via module POM and 
        overwrite any default behavior described below
      - The bundle version is inherited from the project version. In
        case the project version ends with "-SNAPSHOT" it will be 
        replaced with ".qualifier". Tycho's qualifier expansion is 
        supported. Thus, if Tycho computed a proper build qualifier
        then this one will be used as the qualifier replacement.
      - The Bundle-Name is inherited from the Maven project name.
      - The Bundle-Description is inherited from the Maven project
        description.
 4. Final bundle jar is produced.
 5. Source code for dependencies is collected (via sources classifier).
 6. OSGi manifest for source bundle is generated together with 
    OSGI-INF/l10n/bundle.properties for localizable-ready content
    (Keys are bundleName and bundleVendor; inherited from main OSGi
    manifest generated before.)
 7. Final source bundle jar is produced.
 8. p2 metadata is generated (via Tycho p2 plug-in).

Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>