bugfix: Trajectories were putting constant var values directly into function bodies for assignment rules. These were then getting cached, so trajectories would end up with assigned variables at improper values. Fix this by using a call to self.get_var_val to set the constant var values.
bugfix: Trajectories were putting constant var values directly into function bodies for assignment rules. These were then getting cached, so trajectories would end up with assigned variables at improper values. Fix this by using a call to self.get_var_val to set the constant var values.

GutenkunstLab/SloppyCell,GutenkunstLab/SloppyCell