Update Transient Class to all them to be "rerun"?

[jgostick]

I was trying to run a transient algorithm for times 0->1, then update the BCs and run from 1->2, but this soln object was recreated each time, deleting previous progress. It was relatively easy to fix as follows:

if len(self.soln):  # New code
    new_t = np.hstack((self.soln[q].t, soln.t))
    new_y = np.hstack((self.soln[q], soln))
    self.soln[q] = TransientSolution(new_t, new_y)
else:  # Original code
    # Return solution as dictionary
    self.soln = SolutionContainer()
    self.soln[self.settings['quantity']] = soln