EditInsertSignature command needs optional prompt

Many cases (contracts, inspections, applications) require multiple signators, usually committing to a single version of a document. They sign one after the other, as a single atomic action.

We have such a case where multiple signatures are displayed in the final document along with the names of the signators, so we need to match up each signature with the correct signator's name.

To avoid any confusion, we need the signator's name displayed in the signature capture dialog. To do this, the EditInsertSignature needs another parameter to allow for some optional prompt to be displayed. Then the developer can use this parameter to include the name of the signator (or some other prompting text) to be displayed in the signature dialog, above the signature canvas.