Instead of excerpt from /proc/meminfo, use just one integer. This make
qmemman handling much easier and ease implementation for non-Linux OSes
(where /proc/meminfo doesn't exist).
For now keep also support for old format.
FixesQubesOS/qubes-issues#1312
This is part of fixing qvm-start.
qmemman was moved with minimal touching, mainly module names.
Moved function parsing human-readable sizes from core2. This function is
wrong, because it treats k/M/G as 1024-based, but leave it for now.
