#65 Optionally monitors individual cpu cores

[José Romildo Malaquias]

This patch reworks the cpu plugin so that individual cpu cores can be monitored.

The patch:

1) defines a new Gtk+ widget called GtkChart, based on the code of the chart plugin

2) redesigns the cpu plugin, which now uses a box containing a gtkchart widget to monitor the overrall cpu usage, and optionally one gtkprogressbar for each cpu core to monitor individual cores

3) the new boolean option AllCpus is used to enable or disable individual core monitoring

[José Romildo Malaquias]

Optionally monitors individual cpu cores

[José Romildo Malaquias]

It is assumed that the patch 3415996 (https://sourceforge.net/tracker/?func=detail&aid=3415996&group_id=66031&atid=513127) has already been aplied.