Add axis label (requires flot "axislabel" module).
Workaround default axis label color.
Save horizontal space between labels.
Provide minimal interval between ticks so label don't overflow on
each other.
Provide label width for Y axis so consecutive graphs are correctly
lined up.

Also, rename storage to be easier to understand in --help output.

So line count remains visible.

With (hopefully) appropriate settings.

Because graphs are nicer at higher definition, and tables are nicer with
fewer columns.

Also, only execute expensive date parsing when actually rendering dates in
a graph, removing the need for PARSE_DATE.