FE: [refactor] invitation dialog

[cch5ng]

• (moved to BE: [bug] prevent creating dupe invites, contacts #52) use dynamic auth user state to get logged in email
• (moved to BE: [bug] prevent creating dupe invites, contacts #52) define a default route on the authenticated app component (when login succeeds, it should redirect there)
• (fixed in messaging flow setup #65) look at the invitation dialog bug (probably place condition on the request for referralId, like only request if dialog state is open)
• (low) use material ui validation component/styling for input errors
• (low) somehow display error message when the invitation send button is clicked and an error results (json returns the error but nothing is done with it now); try to be consistent with the login component
• (low) try to fix the positioning of the copy button; right now the css position is pretty brittle so if time, try to save btn as svg and use custom icon, placed within input for more consistent placement