Graphing support in API client and export

[kiddinn]

Is your feature request related to a problem? Please describe.

1. When exporting the content of a sketch, saved graphs are not included.
2. There is no graph support in the API client

Describe the solution you'd like
Add a graph.py file in the API client that implements a way to interact with graphs.

Additionally add support for exporting graphs in the export API call.

[kiddinn]

API client now supports graphs, but graphs are still missing from the export