Re-implement Chart DB

[liversedge]

Need to move away from GCP and reimplement on self-hosted basis.
Will move the release date to End of January to allow this to complete since its a big change.

[liversedge]

Lets make this more extensible, so we can use it for more things in the future:

1. Sharing Charts
2. Sharing Perspectives (Sets of Charts)
3. Sharing Metrics
4. Sharing Workout Files (ERG et al)
5. Sharing Training Plans
6. Sharing Trainer Config (Virtual Curves)

[liversedge]

If we create a backend API there is nothing to stop us creating a website to browse it for non-GC users. But that will likely come later.

[liversedge]

Moving to 3.7, it will take too long to implement and better to do alongside v3.7. Moving the release date back to the end of the year.