different zoom speeds with finger and wheel on different browsers/OS

[ens-ds23]

Zoom scrolling is horribly and unpredictably variable across browsers: there are no standardized units. This is mainly a problem:

1. where some browsers are incredibly "quick" (eg physical mouse + firefox + linux) which not only makes it very difficult to control it also stresses the code performance;
2. where some browsers are incredibly "slow"(eg physical mouse + chrome + linux) where zooming in and out are a slog.
3. most things involving two fingers and trackpads are sensible.

Mitigations could include:

1. a "speed limit" which would help prevent excessive zoom speed allowing us to veer in one direction for our settings;
2. browser sniffing (don't want to do this);
3. working out what kind of device we have from zoom acitons which we've seen so far (ditto but probably less bad);
4. "minimum speed limit" (not sure this wouldn't be annoying);
5. advanced browser API yet to be discovered.