Add osgi manifest to jar.

It is very easy to add and would be a great help for all osgi users. Here a example maven plugin config taken from the google guava pom.xml:

``` xml

org.apache.felix
maven-bundle-plugin
2.3.7


bundle-manifest
process-classes

manifest





!com.google.common.base.internal,com.google.common.*

javax.annotation;resolution:=optional,
sun.misc.*;resolution:=optional




```