Serious Lag expanding Niagara river (and others) due to graph

[ecc521]

The Niagara river (https://rivers.run/#Niagara%20Fort%20Erie) reports data extremely frequently, so graph contains several hundred points. This results in a multi second lag opening the river view once full data has been loaded (the initial load is only a few data points, so works at normal speed. Once full data is loaded, full data is drawn on future openings, resulting in heavy lag)

[ecc521]

This is now significantly more important with the NWS gauges - offscreen canvas should probably be used

[ecc521]

d1d5a1c massively mitigates this issue, making it far less catastrophic. Backgrounding should be done, but it is now an enhancement, not a critical issue.

[ecc521]

This issue is more serious with additional USGS data as of 0ccaf5e, and impedes the potential addition of more data (like 7 days)

[ecc521]

Accidentally closed - reopening