With this, the page does not move to the searchbar each time you click on a subject.
Added __hash__ so a set can perform meaningful operations on Lesson
First batch of tests to test the capabilities of the updater (the updater picks which Lessons have been discarded and / or added between updates)
Solved bug that made possible for Lesson __key() not to be unique. I hadn't thought that the date info is not included in the raw_data atribute.
Updated tests