First bunch of changes, all rebased into one.

Fixes:
- Sysstat version detection
- Detect and show Bps/kBps depending on sysstat version
- Auto-add -T option to sadf>=10.0 for epoch seconds
- Detect whether sar -r or -S is required for swap stats
- Label on context switches
- Fixed slightly confused walking of history

User Interface:
- Actively and silently skip non-existing SA files
- List possible metrics when non-existing metric given
- Hide line label in graph, as we only have one line
- Attempt to make x axis labels somewhat more readable

Cleanup:
- Indenting when parsing arguments
- Default setting for metric
- metric variable no longer changes its role mid-script
- Add my name to the list of authors. ;-)
- Change load average to 15-min average, because sysstat
  by default does 10-minute intervals