Rename top(1) to mtop(1), import NetBSD top(1)

Due to differences in (mainly) measuring and accumulating CPU times,
the two top programs end up serving different purposes: the NetBSD
top is a system

Rename top(1) to mtop(1), import NetBSD top(1)

Due to differences in (mainly) measuring and accumulating CPU times,
the two top programs end up serving different purposes: the NetBSD
top is a system administration tool, while the MINIX3 top (now mtop)
is a performance debugging tool. Therefore, we keep both.

The newly imported BSD top has a few MINIX3-specific changes. CPU
statistics separate system time from kernel time, rather than kernel
time from time spent on handling interrupts. Memory statistics show
numbers that are currently relevant for MINIX3. Swap statistics are
disabled entirely. All of these changes effectively bring it closer
to how mtop already worked as well.

Change-Id: I9611917cb03e164ddf012c5def6da0e7fede826d

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