Better summation table formatting

- In Isolate transform, use `,.3f` format - there’s room for more data
- Make `summation_table` formatting consistent with
`timeshift_summation_table`
Consolidated action model and action registry
Refactor actions registry into a generic registry module
Add a transform registry and simplify transforms

They don’t actually need to be observable model objects - simple
objects will do just fine
Merge pull request #233 from urbanairship/transforms

Transforms cleanups & registry code consolidation