Switch from base_ to slot_ where possible

[wmwv]

After discussion with the LSST DM DRP team, I have a clearer view that slot_ is what is supposed to always be there. base_ is how it was done. We in general should use slot_ columns when preparing the Object table. There were some measurements missing in Run 1.1 which meant we didn't do this.

1. Take another look at the existing Run 1.1p translations to see what can be done with slot_
2. Check Run 1.2p processing to make sure the slot_ columns are all filled in now.

[yymao]

@wmwv Is this issue still relevant? If not we should close it. If it is still relevant, feel free to change the priority (I am currently assigning it a low priority).