Add more form properties

[yanokwa]

I love the return of form properties! And that return reminds me that http://xlsform.org/ref-table/ under the settings, as some form specific options that we should consider.

• public_key for encrypted forms
• submission_url, mostly for Google Drive support, but folks do use it to submit to a different server than the form was downloaded from.
• instance_name to name submissions. There could be some clever UI where you build the name by choosing from the list of data names.
• version for versioning. We might want to move the timestamp that build puts in the form id here and then give folks the change to override.

[issa-tseng]

I'm wrapping a fix to form_title to account for Form Properties "Title on Device" into this ticket.

[issa-tseng]

Okay, so all of these also necessitate changes to Build's own XML output. For version, should that only be applied to orx:version (which we currently don't output at all), or also to instance id? And if we want to modify id, should the entirety of id be equal to version or just the timestamp suffix we currently apply? What if the user supplies an invalid version and this breaks id?

I maybe propose we implement the rest of these and kick version down the road a little bit, unless you have strong answers here.

[yanokwa]

I like the proposal of punting on version for now because it feels like a longer conversation. I've started a discussion with some of the key players here: https://forum.opendatakit.org/t/how-is-version-used-across-the-ecosystem/8964