Fix plotting series when the first data point is empty

[tonyhignett]

• Add graphql to the dependencies, to help interacting with the schema.
• Get the schema in parallel with the first data query and remember it.
• Use it to find the numeric fields under the data paths, instead of inspecting the first data point.
• Fixes #45

[retzkek]

Awesome, thank you! Sorry I haven't had a chance to review this yet.

Going to be a bit tricky integrating this and #60...

[SydoxX]

In #60 I tried to keep most of the non-requesting code the same so most of this stuff can be layered on. But RequestFactory will need some rewriting. I'd say we merge #60 first and then cherry-pick the conflicting lines, there shouldn't be too many of them. I'm happy to help with merging.