daemon: Zero unlimited memory limits in CGroupMonitor

When memory cgroups have no limit, they set to MAXUINTXX of the number
of bits of the platform. This is much easier to detect in C code than
in javascript, so set these to zero (ie: no memory limit) in
CGroupMonitor.

Because this is platform depend
daemon: Add tracking of CPU shares into CGroupMonitor

This lets us see changes in this setting.

As we noted earlier our cgroup monitoring scheme needs so me fine tuning.
And we don't try and do that here.
web: Load default Memory, CPU, and TTY run settings from image config

Closes #379
web: Refactor sliders into MemoryLimit and CpuPriority objects

We want to use these sliders in multiple places. make them real
objects, albeit private to the docker code.
web: Read Docker container memory limit from CGroupMonitor

It could have changed since the container was launched, so don't
use the container config. We want to be able to react to changes
in the system appropriately.
WIP changeable cpu resources
WIP and its working
WIP use DBus to run the command
WIP show CPU shares