plotStates: Plot state variables
In dkneis/rodeoApp: Interfaces for Rodeo-Based Models

Plots the simulated dynamics of state variables.

1 2	plotStates(out, out_old, timeUnit, timeBase, model, mult, show, rangeT, rangeY, gridT, gridY, logY, labelY, showOld, obs)

`out`	Object returned from latest call to `simul`.
`out_old`	Object returned from an earlier call to `simul`.
`timeUnit`	Unit of numeric simulation time info (as a string).
`timeBase`	Date and time of the startpoint of the simulation as a value of class `POSIXct`.
`model`	Object of class `rodeo` representing the model.
`mult`	Named vector with multipliers to apply to variables before plotting.
`show`	Named logical vector to enable plotting of individual variables.
`rangeT`	Range of the x-axis (time axis).
`rangeY`	Range of the y-axis.
`gridT`	Logical to enable/disable grid for x-axis (time axis).
`gridY`	Logical to enable/disable grid for y-axis.
`logY`	Logical to switch between linear and log axis.
`labelY`	Y-axis label.
`showOld`	Logical. Enables/disables plotting of data in `out_old`.
`obs`	`NULL` or a data frame with observations (numeric time info is expected in the first column).