Reformulate the purpose of the project in README

[lefou]

Especially:

• Remove Karaf of the technology stack
• Make it clear, that it is some kind of out-of-the-box lightweight ESB, that just needs some configurations
• Remove the "general purpose" character, but tell, that it can be used as a basis for other OSGi Apps that base on the same technology stack

Later, we need to provide a tutorial, that shows who Blended can be configured.