Accept an instance for editing

[lognaturel]

User story

As the manager of an ODK project
I want to use Web Forms to edit existing data
So that the edit experience can happen in the same context as the data capture

Notes

• Move instanceID to deprecatedID when editing existing instance #37 (OpenRosa spec) is needed for edits
• odk-instance-first-load should NOT fire
• Some question types, notably geo questions, would benefit from a different edit experience
• There's the possibility for unexpected behavior, especially around non-relevant values which won't be in the instance. Non-relevant repeat instances are particularly an issue because positions may have shifted (see Clarify initial XPath expression context of bind expressions (and similar) #137 (comment) for some related ideas)