Fixes #17, Fixes #18;

- Update XPI to Addons SDK 1.17.
- Request dataPoints with a single request only when the use click on
the class icon.
- Sort points by score.
- Update install instructions.
- Clean up code.
- Make all tosdr.org requests over HTTPS.
Groups TOSDR API calls in a mediator function

Groups all TOSDR API calls in a seperate TosdrMediator function. This is
a refactoring and does not change any behaviour.