aggregation and ipmi plugin support, fixes

New:
- "aggregation" plugin support for "cpu" type.
- "ipmi" plugin support.
- "svg" graphics output option.  This works best when mod_deflate on apache httpd is set to compress files of type "image/svg+xml".

Fixes:
- Add single quotes around any "rrdtool graph" option which can have spaces.  Improves support for RRD files with spaces in the filename (common for SNMP and IPMI RRD files).
- Add some sizing magic for svg file support.  SVG image tags will have "width" attribute added. The width is calculated using a magic number to make svg output approximately the same width as png output, without having to adjust the width and detail-width options in the configuration file.
- Any <img> tags which display RRD graphs are now class "rrd_graph".  This should lay groundwork for using jQuery to auto-refresh those images later.
-  Move logic for padding out labels in LINE1 statements out of the parse_ds_names() function.  This fix makes it so that all labels are padded out with spaces to be of equal length instead of just some.