Refactor interactive microbenchmarks

Replaces the SystemServer Benchmark activity with one that has
several sets of benchmarks grouped into categories. This will make it
easier to add more benchmarks that do not logically fit with the
categories we already have.

This does not remove any of the other benchmark activities, but in a
follow up CL, we should remove those since they are covered by the
Interactive Microbenchmarks activity.

This also does not adjust the non-interactive mode, which should also
happen in a followup.

Change-Id: I1d079362df0d32642525ede5b41779d76a5735ec