Support submission management

[florianm]

Feature

Add missing API endpoints:

• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/submissions/retrieving-submission-xml
• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/submissions/creating-a-submission
• https://odkcentral.docs.apiary.io/#reference/submissions/submissions/updating-submission-data
• https://odkcentral.docs.apiary.io/#reference/submissions/submissions/getting-an-enketo-edit-url
• https://odkcentral.docs.apiary.io/#reference/submissions/submissions/retrieving-audit-logs
• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/submissions/listing-encryption-keys (refactor from submission_export)
• https://odkcentral.docs.apiary.io/#reference/submissions/submissions/listing-submitters

Attachments

• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/'-attachments/downloading-an-attachment
• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/'-attachments/uploading-an-attachment
• https://odkcentral.docs.apiary.io/#reference/forms-and-submissions/'-attachments/clearing-a-submission-attachment
• Assign to family submission-management

Comments

• https://odkcentral.docs.apiary.io/#reference/submissions/comments/listing-comments
• https://odkcentral.docs.apiary.io/#reference/submissions/comments/posting-comments

Versions

• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/listing-versions
• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/getting-version-details
• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/getting-version-xml
• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/listing-version-expected-attachments
• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/downloading-a-version's-attachment
• https://odkcentral.docs.apiary.io/#reference/submissions/submission-versions/getting-changes-between-versions

[florianm]

Working example by Chrissy Roberts on the ODK Forum: https://forum.getodk.org/t/download-audit-of-edits-on-central-using-r-ruodk/37928