User agent not saved for submission edit via OpenRosa

[matthew-white]

Steps to reproduce:

• Create a submission.
• Edit it using the OpenRosa API. Enketo may be the easiest way to do that.
• Request the submission using the REST API.
• Observe that currentVersion.userAgent is null.

From a quick look, it seems like we don't pass the user agent to Submissions.createVersion() for a submission edit via OpenRosa. Compare:

Via the REST API

central-backend/lib/resources/submissions.js

Line 198 in e9dba19

Submissions.createVersion(partial, deprecated, form, query.deviceID, headers['user-agent']),

Via the OpenRosa API

central-backend/lib/resources/submissions.js

Line 93 in e9dba19

Submissions.createVersion(partial, deprecated, form),

[matthew-white]

From the above, it looks like the device ID is also not saved for a submission edit via OpenRosa. However, Enketo doesn't send a device ID, so in practice that isn't really an issue. (At least for now: Enketo may start sending a device ID.)