feat(timetable): provide a builtin reducer for parsing lessons automatically

[Vexcited]

Default behavior of the lessons given by the TimetableOverview is to return the raw parsed lessons. Meaning that it just iterates through the data given by Pronote and gives you back an array of parsed objects.

Even though, it doesn't handle updated lessons, etc. so to fix this, we might add an extra reducer function that can be added on top to make sure data is well parsed.

Fixes this issue : PapillonApp/Papillon#113