Allow inviter user to request that the signatures are added in a certain order.

[enriquepablo]

So when creating the invitation, only the 1st invitee will be informed by email of the invitation; and only once they sign the document, will the 2nd be informed by email of the invitation; etc.

Controlled via a checkbox in the invitation form, and keeping the order in which the invitees are added to said form.

This can take around a week to implement