Make lasso tool work on other plots

[bethac07]

I recall that that there is a technical reason why it currently is only supported on the dimensionality reduction plot but could not find in 5-10 minutes searching here plus Slack what that reason is. Let's document that here for future potential improvers :)

[DavidStirling]

The main reason is that the other tools all use a custom navigation toolbar which we reconstructed to look like MatPlotLib's, since there used to be a bug breaking the native wx toolbar. Getting Lasso support will require us to replace that messy toolbar code with the newer solution, plus a rewrite of the (largely unused) 'selection' feature in those tools.

I think it only really makes sense to enable Lasso in the Scatter tool, so it's not a huge amount of work, but we wanted to see whether people found it useful before doing such a rewrite.

[vladimirvig]

I would definitely find this useful because the current selection option (filter+gate) pulls out all the cells that are not on the plot (thereby ignoring the filter setting) in addition to the target ones. (I created an issue for that, too.)