Get scaled traces for SpikeSortingView

[khl02007]

Sometimes the spikeinterface recording object is in analog-to-digital converter units rather than physically meaningful units like microvolts. In that case, the recording may have gain parameters that can be applied during calls to get_traces to convert the traces to physical units. This change checks if such parameters exist (by calling either has_scaleable_traces or has_scaled methods) and sets return_scaled parameter of get_traces to that.

[magland]

@khl02007 I'm fine merging this as long as you've tested it on your end.

[khl02007]

Just tried running my branch on two recording objects, one with scale specified and one without. It seems they both run and are the same except for the scale in the spike amplitude view

[alejoe91]

Looks good to me too @khl02007

[magland]

Now published as 0.13.5