Start a new module for benchmark. Implement SorterStudy that replace GroundTruthStudy

[samuelgarcia]

This is continuation of the work presented by @yger in Edingurgh workshop : faster and easier benchmarks.

This PR:

• create a new module for spikeinterface.benchmark
• replace GroundTruthStudy by SorterStudy. similar API but not backward compatible.
• move the BenchmarkStudy and Benchmark base class from spikeinterface.sortingcomponents.benchmark
  to spikeinterface.benchmark
• move all components benchmark to the same submodule
• refactor plotting to share plots across benchmarks
• remove plotting related to benchmark in spikeinterface.widgets

[samuelgarcia]

@chris-langfield and @cwindolf
if you are doing benchmark for dartsort you should have a look to this.