feat(invite-friends): add inviting friends via email. URL parsed, session holds invitation. If user joins party (new user or existing), the inviter is rewarded
fix(intive-friends): only invite set invitation if user hasn't already
been invited to a party
fix(invite-friend): change variables
feat(invite-friends): update wording on invitations. Add commented-out
sample code on copy-link (it's not working)
Merge pull request #4238 from HabitRPG/invite-friends

Invite friends