ISO8601 phase one: serve raw temporal data

[ggalmazor]

Problem description

Aggregate parses temporal data to Date objects, moving the temporal data to the server's time zone in the process.

Since the original time zone offset is lost, all the downstream views of temporal data aren't exactly equal to the originally received data. This affects:

• Download submissions servlet
• Submission exports (CSV, JSON, and KML)
• Form publishers (Google Fusion Tables, Google Spreadsheets)

Expected behavior

Aggregate should always serve temporal data in exactly the same form as it was received.

A PR solving this issue should have to explain:

• how temporal data is stored from now on
• how Aggregate is backwards compatible with forms uploaded before this PR
• how does it work with new submissions arriving to forms uploaded before this PR
• Any workaround users could use to "upgrade" their forms.

Other information

Refer to this document for more information and context about ODK's ISO8601 adaptation effort