Create appointment within weekly calendar

[jollopre]

We need to offer the functionality of creating an appointment within a weekly calendar.

• Tapping/clicking on a calendar area opens a view where starting_at is already filled and a default of 30 min duration is set.
• New appointment view should have a typeahead to choose the customer, dropdown to select the offer, dropdown to choose the duration (30/60/90/120 min) and a calendar with date/time.
• Request test for new appointment
• Feature or integration test for creating an appointment