Create workshop type

[kevinsimper]

There should be a special workshop type that allow custom behavior
It should check the capacity of the workshop

One graphql mutation will be attendWorkshop. That will check:

• is there space left
• has the event passed

[kevinsimper]

Have begun working on it here
#436

We need a way to get a list of workshops first.

[kevinsimper]

A workshop has following properties more than events has (at the moment):
price
maxAttendees
questions

In first iteration you will be able to make a free workshop and attend.
In the future version you can apply to attend a workshop, because it is not sure you should attend if it does not fit.