generate OSGi manifest when creating JAR file

The best way to use custom encoders/appendes in an OSGi environment is
to create fragements which attach to the Logback Classic bundle. This
makes the classes available to the Logback Classic bundle for
class-loading.

Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>
ignore plug-in in m2e
Merge pull request #1 from AGETO/osgi

Add OSGi Manifest Header Generation