The link button to add a new application member to an app that did not
have any ("empty state") was not wired up. This:
- Moves the two steps of the new member modal into macros so that they
can be reused with different button/link types
- Wires the "invite a new team member" button on the application team
page
- Makes a minor CSS tweak so that icons nested under `.empty-state` in
the modal aren't enormous
f974dab330