Added "tracker dev" boolean field to Member

Now, being a tracker dev is independent of the linear role system, meaning that alumnis can be tracker devs without being marked as "active" members (and therefore they will not show up on the tshirt order page).

Regarding role elevation, only tracker devs can mark people as tracker devs. This has been hardcoded and does not go through cancan.

The roles for egarbade, krauchen, merichar, mreiss, abtech and treid have all been manually assigned.

refs #136