Streamline text and parse data upload scripts

[akprasad]

They were made for an era when I was developing locally and production was expected to be unstable. It's cumbersome to add texts and far too easy to break production.

At a minimum, these scripts should:

• run idempotently
• run non-destructively (e.g. the current gretil seed script naively drops and recreates texts, which also means it drops their parse data).
• display their actions in a clear, user-friendly way
• run as part of every deploy without needing manual intervention

[akprasad]

For texts, see #291.