Generate time series graphs from pbench .csv files

*generate-pbench-timeseries-graphs* -- generate graphs from .csv files
from Pbench raw output

Usage (for now): `generate-pbench-timeseries-graphs [files...] | bash`

Lots of TODOs:

1. Command line arguments for image size, max # of data sets, what else?
2. Actually feed the output into gnuplot rather than just sending it to stdout
3. Optionally sort data sets by max value or max average
4. Combine multiple samples into 1.
   This will require that generate-pbench-timeseries-graphs enumerate the files
   (or accept the file list on stdin rather than command line) because the command
   line won't be able to accept all of the files in a data set.
5. Handle .csv files from perf and any other tools I've missed.
6. Allow scaling of Y and possibly X axis.
7. Allow command line override of per-file settings.
8. Allow additional gnuplot options
9. Error checking
10. Make data max/minvals available to graph generator so that it can set
   the axis bounds in gnuplot correctly.
11->Graham's number ...

Author: RobertKrawitz