Allow to show meetings in the calendar

[ClemensRobbenhaar]

The Calendar Application should display also all the meetings from the Meetings Application.

Must have:

• optionally allow to show meetings in the calendar

• show the meetings in the date range used by the current calendar

• limit the range of meeting details shown in a way "reasonable" for the current calendar.

• allow to access details of every meeting from the calendar (at least via link to the meeting details page)

• does not break if the meetings application is not installed

Should have:

• optionally limit the meetings shown in a calendar to the ones in a given (different) space
• ability to move meetings in the calendar
• ability to edit meetings in the calendar

[mflorea]

Fixed with 32b3bb4, 94a524b and d2fe7b1 .

[lucaa]

Fixed with 32b3bb4, 94a524b and d2fe7b1 .

A bunch of (other) commits were done for this ticket and tagged with #47, so if all commits for this work need to be discovered, that issue is a good source of information.