Better filetype handling. More error checking

plot.py now has an additional bit of error checking. plot.py
currently relies on the option --scanind being used with
calculate.py. If the error associated with that missing occurs,
it lets you know.

Can now save to multiple filetypes at once.
Fixed error with importing MM3* angles

The value for param_type was wrong for MM3* angles (equilibrium
values and force constants) and the value for mm3_col was wrong
for the angle force constants.