Fixed MemoryPoolsGraph time resolution

Jolokia returns timestamp in seconds, while the graph expects
the timestamp to be in ms.
This causes the x-axis in the memory pools graph to be
completely confused.

I multiplied the timestamp by 1000 to make it fit the format
jqplot expects.

Fixes #73.
Merge pull request #78 from dzautner/fix-memory-pools-graph

Fixed MemoryPoolsGraph time resolution