Modify unit tests

[rklasky]

1. Some unit tests show a 0 output biomass

Modifying the ForcedMigrate parameter with either random or stepped noise causes the output biomass to be 0 when running an RK4 simulation. This also happens with ForcedCatch for Seals but with an AB simulation. Use noise variations of no more than 10% around mean of existing forced parameter (i.e., catch). Add noise of only +-10% of mean around forced parameter in question.

2. Save current-baseline differences as output data files in addition to the .pdf containing all of the plots.

3. Allow user to choose between a) showing current and baseline plots superimposed on the same plot or b) showing only the difference of current-baseline plots on each plot.

4. Add Unit Test Vignette

5. Add JuvRoundfish1 and AduRoundfish1 species groups.