Better timestep output, injection wells work, and fixed rate bugs

I think the final part of #1 will be to check that Qw is calculating
correctly (10%*Qw_1 is never reached, so Qw_2 might be accidentally
Qw_2) and to complete the Excel output steps (P[,] is outputted, but
Qw[,] and Pwf[,] need to be as well).