feat(more complex filters)

• Added denormalized data about semesters, majors and minors in university model

• added function to compute it

• Added function to cron

• new FilterHandler in the front to handle / cache the filtering

• Tweaked map and search components to display the right stuff

• Map now displays in a different color the elements that have been filtered

• Renamed spacilities field to majors

• Fixed bugged in downshift multiple (couldn't add same after delete)

• Deleted useless code in offer

Linked to #31