Display member count

[otytlandsvik]

✨ Member count should be displayed in admin members view

Every semester, NT-SU needs a list of our active members. This count should be calculated and displayed on the admin>members page.

💫 Caveats

There are some potential caveats:

1. Only active members should be displayed
2. Members who have registered before for example 2018 should not be counted here, as these are not yet set as inactive automatically
3. Some people have multiple users (maybe forgotten passwords?). This may be out of the scope for this issue though.