Simplify MemberView by fixing size instead of calculating it dynamically

Gijs Hendriksen
2018-01-24T20:49:55+01:00

### Short description
Simplifies the `MemberView` and `SquareView` by giving it a fixed size instead of calculating it upon layout. This makes it easier to show a list of members, for example with an event with registrations, as you can now simply use a `FlatList` with 3 columns.