Added mem_free to graph.d/mem_report.php graph. Was present in ganglia web 1. Also ported RGB color definition from there.

Reason:
Displaying memory graph for linux works as expected, but metrics from windows
Host sFlow agents displayed swap usage where free memory should be displayed.
Therefore it presented itself as when machine has all of it's memory and lots
of swap space occupied, when that was clearly not the case.

This change adds it back to graph stack and also displays now/min/max/avg
values in the legend.
Provide the option to remove unnecessary XML data.

The EXTRA_DATA and EXTRA_ELEMENT data returned by Ganglia is unused in
many code paths, so by stripping it we can see XML parsing performance
gains of about 50% for large data sets.
Fixed a bug in the view tree
Fix error in the display of the show-hosts buttons. The Auto and Same buttons were reversed.
Merge pull request #241 from pcpiela/master

Fixed a bug in the view tree
Merge pull request #240 from cddude229/optimize-xml-volume

Provide the option to remove unnecessary XML data
I don't even
Merge pull request #238 from bostjan/bugfix/report-graph-mem/add-free-mem-to-stack

Added mem_free to graph.d/mem_report.php graph...