Add possibility to convert between units for plot

[pineapple-cat]

Units for each axis in a graph are specified within a config, and one of the specification options is to enter a column name to extract units from. Currently, if all the rows in the dataframe to be plotted do not have the same unit, an error will be thrown.

This is not a pressing matter, but it could be useful to allow unit conversions at some point. For example, if all units share the same base unit (such as flops/s) but differ in magnitude (Mflops/s, Gflops/s, Tflops/s, etc.), they could all be converted to one magnitude. Or, if a custom unit label is specified alongside a column name, the plotted data could be converted to the custom unit.

See libraries such as pint or units.