Issue10

[tvirolai]

This PR fixes issue 10.

It contains the following changes:

• Flask has been upgraded to Connexion
• The API specification is mapped to the code and the Swagger UI works (although not all of the specified functionality is implemented yet).
• The directory structure has been changed a little bit. The only way I could get the imports working everywhere was to move the stuff from the directory ./annif to the project root.
• The annif.py file has also been refactored a bit. After struggling a little bit with how to call the functions both via the API and the command line, I separated these tasks to different functions. For example, the function show_project now returns JSON when called via the API. When called from the command line, the click command 'show-project' calls another a function that calls 'show_project' and parses the response to a human-readable string. This works and I think this separation of concerns makes testing easier in the long run. Dunno how elegant a solution this is.

[osma]

Looks good! It's definitely a big step forward so I think we can merge this.
I hope we can find a way to restore the directory structure so that we don't need to have annif.py and other Python scripts in the root directory, but it's OK for now.