Slowly deprecate old PowerAnalytics

[GabrielKS]

The current migration plan, as developed here:

1. Release new PA, keep old PA as is
2. Develop a user base on new PA, fix some bugs
3. Deprecate old PA (i.e., throw warnings) but keep it so PG can use it
4. Revamp PG to only depend on new PA (I would be interested in supervising an intern to do this)
5. Remove old PA

but not committed to that, open to discussion.