The heart of this fix is to change the "My Team" view to use a
collection of teams instead of memberships. The team card is
refactored to only take a team, rather than attempt to be polymorphic
over teams and team memberships. This change enabled removing a good
amount of old code. This also requires adding a `username` parameter
to the teams list endpoint which allows getting a list of all teams
for a single user, in order to allow refreshing the "My Teams" view
correctly. Currently this list is of length at most one.

TNL-3410