[Feature] Add calendar view

[pylapp]

Is your feature request related to a problem? Please describe.

As we can see in the in-dev web front, there is a calendar to display the available slots to get shots.
The UX is better, and we should have something similar in the iOS front. The calendar will be, or is already, available on Android and web platforms.

Describe the solution you'd like

See Android et web fronts to have an idea of what could be the calendar.
A big refactoring of the UI (cells, delegate, view controllers, xib) should be done, that is the reason why we should deal all previous pull requests before.

Describe alternatives you've considered

Nope

Additional context

Nope