Move web service documentation to doc/developer

Added documentation directory with subdirs for developers and users.
All developer related documention such as implementing services or
architecture descriptions should go to doc/developer. All user related
content such as installation manuals or handbooks should go to doc/user.
Copy decription README from 1.8.x
Merged ActiveMQ doc into single Markdown file
Add documentation stub for Goobi Module API.
Added German installation manual stub file
Started documentation for JAX-RS API
Fix formatting issues
Fix character escaping in headers
Merge pull request #16 from goobi/docs

Starting point for improved API documentation