Support for auto-send and auto-delete

[lognaturel]

Form-level directives for auto sending and/or auto deleting were recently approved at the XForms spec level: getodk/xforms-spec#100

There isn't yet an approved syntax for XLSForm: XLSForm/pyxform#126

[florianm]

XForms spec: https://getodk.github.io/xforms-spec/#submission-attributes
Example: <submission orx:auto-delete="true" orx:auto-send="false">
Former blocker XLSForm/pyxform#126 is now closed (Issa's comment hidden as outdated ;-) )

Where in the UI should these settings live? Menu > Edit > Form properties is the closest in scope.

[florianm]

Solved my confusion (https://forum.getodk.org/t/help-me-understand-xforms-auto-send-delete/36290) and took at quick stab at this while the babies are asleep.

Form Properties:
Default is to Follow ODK Collect. Nothing gets inserted into the XML.

Selecting "always" or "never" adds the relevant submission attributes to the XML.

XML exported:

The auto-send/delete settings get saved and restored on form load.
The input (select) needed to be added to the CSS style.
Added to the currently open PR #266.

[florianm]

The "select" input could use a dash of bottom margin to make the spacing to the help text identical to the text inputs.
Edit: Dash of bottom margin applied in 2a84f90 but tagged wrong issue because I have the clumsies