this patch adds two classes for the charts:
RRDStore:
based on our updatestore, but specialized on our rrddata output
it converts the percentage (cpu) and the time (from unix to milliseconds)
also it handles the changes for the timeframe and cf
it sets a default reload of 30seconds
RRDChart:
based on Ext.chart.CartesianChart,
with specialized options for our rrd graphs
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>