Updates the invite modal so that if the custom input is 0, the
submit button is deactivated, since an email invitation or invite
link that immediately expired would be unusable.
Also, updates the custom input to show 0 if a user navigates away
from and back to the custom input option afer putting in an invalid
value, e.g. "abc" or "-20". Previously, the custom input showed
"NaN" in that case.
We now mention if user is member of the group in the "Members"
tab, also including the details about whether the user is direct
member or is member by being direct member of one of the subgroups.