Make measurements sortable

[rolandgeider]

Part of the health sync issue wger-project/wger#2417

Since we will have many more measurement categories, many of which we don't know in which order they will be created, we need to add a way to sort them. I propose a simple UI like we do for the dashboard in the mobile app where we show a list with names and sort that.

Note that this needs a new "order" field in the backend