Implement jBPM client API for jBPM3

• ThomasD + HeikoB design the BPM API in the jBPM3 SVN
• TomB reviews,comments,approves API
• ThomasD implemts the API on the jBPM3 code base
• HeikoB implemts the API on the jBPM4 code base

On our way to jBPM4 we promise backward compatibility of API and process descriptors. Necessary changes in configuration will be documented. Database structure and content may change in an incompatible way.