Create wro4j-osgi bundle

This pull request makes it possible to use wro4j servlet filters inside osgi environments. 

The new wro4j-osgi module uses the maven-bundle-plugin to add the required metadata to the manifest in order to create a valid wro4j-osgi bundle jar that can then be used inside osgi. 

A workaround is provided so that SPI calls (such as ServiceLoader.load) will work correctly inside osgi's more restricted classloader rules. This allows wro4j to find providers inside osgi.

This has been tested inside Apache Karaf 4.2. 

As an added bonus for development time, if you use "file:" uris to define groups inside wro.xml configuration, then when js and css files are edited, the changes will show up instantly (no rebuild and/or redeploy into osgi required). 

Please see wro4j-osgi/README.md for more