Re-integrate the activation delay for uniswap oracle

[thomas-waite]

Summary

The Uniswap Oracle has an activation delay of 24hrs hardcoded into it. This was removed for the purposes of the hackathon submission - didn't have time to wait 24hrs for it to activate!

TODOs

1. Put the activation delay back in and a deployment pipeline setup which anticipates and accounts for this when pushing updates.

2. Update test fixture to fast forward 24hrs by default - the tests are written as if the 24hr delay is on the contract. However this could also be cleaned up, as we call a specific context contextForOracleActivated() for each unit test that relies on the oracle activating - it should be the default, rather than the specific exception.

3. Find an automated way of calling await oracle.update() every 24hrs