Make (memory) limits human readable

Right now, Isolation section shows everything as in MB, which is really hard to understand. Start to use the ByteSize type (from http://golang.org/doc/effective_go.html#constants) to make them more human readable.
We actually only want the "unit-label" class applied to the units. We can either separate the unit printing from the number printing or remove the use of "unit-label" completely.