Add additional widgets for the CPU

[xxxserxxx]

This is spawned from #17

Provide an alternate view for the CPU data showing per-CPU values.

The current view is per core; that is, every label CPUn represents a CPU core. Users have asked for a view common to some other usage tools, that is a per CPU view where the usage is a sum of the cores in the CPU.

While I'm not interested in displaying paradoxical values > 100%, I'm willing to provide it. The CPU displays will be:

1. Current, per-core or average only display
2. Per-CPU, core-averaged display
3. Per-CPU, "total" display

Each view will allow the AVG label and value, for all computing value in the machine.

1 - ∑C/Δt (actually, it should be a rolling average over a time window, so slightly more complex than that)
2 - ∀p, (∑C_p) / (|C_p|)
3 - ∀p, (∑C_p)