Extension:CentralNotice/Notes/Miscellaneous doc bits

A place to note down things that should go in proper documentation, when we do that.

Cache TTL

We should be very clear on the cache lifetimes of:

• Campaign choice data
• Banner content

CAMPAIGN_STALENESS_LEEWAY

Constant in bannerController.lib.js. Determines leeway for considering a campaign received via choiceData to be stale.