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.
Fix URLs
Refactor TOSDR API calls
Update XPI
Merge branch 'cimm-tosdr-mediator'
Extract service update logic

Extracts the service update logic to a seperate function so the
`main.js` file does not need to calculate dates, it can simply ask the
UpdateTracker if it needs to fetch the updated services list.