Code reorganization and further fixes regarding http handling

This continues pull request #32 opened by @skanct. Quoting: 

"This is an initial attempt to reorganize the code base of ar-web-api. It is not ready to be merged yet. The reason that I am opening the pull request is to trigger the discussion.

Goals:

Consistent structure
Consistent naming
Identification of common functionality"


Further it introduces views in all packages, adds proper error handling, adds json marshaling in AR results, introduces proper http header handling and adds http return codes more consistent with the RESTful style. 

Future work: 

1) add json responses for profiles and recomputations. 
2) remove duplicate code in the extent of the project