CPU usage bar does not handle multiple CPU cores

[pulkomandy]

When you have multiple CPU cores, Slayer will measure CPU usage vs. the total available horsepower. This means a single thread can never go past 25% on a quad core machine, for example.

This should be reviewed so:

1. Threads show their percentage of use for 1 core, which can go from 0 to 100% (hogging one core)
2. Apps show their usage of each of the available cores. The single bar could be replaced by 4 thinner ones, for each CPU.