Merge develop to master

See merge request !4

Add Helpers class

Remove index in td

- Close modal after sharing timetable
- Don't create a message if either from user or from timetable id is empty

- Reload page after creating a new timetable
- Don't get busy days of a deleted timetable

Make logo become clickable

Update logo
Update CSS

- Merge 2 timetables together and show available days between those
- Integrate HTML
- Update CSS
- Update Firebase query to deal with the messages and timetables

- View timetable
- Create a new timetable
- Update an existing timetable
- Doing sharing function

Merge frontend to develop

See merge request !3

Implement Google Sign In
Revert the HTML integration, need to do it later

Features/sign in

See merge request !2

Features/signup with email and password

See merge request !1