Updated temporal driving functions comments and added missing ls
Removed some of the conf dependencies

For example if you have set conf.usehpre=false, it should be not neccessary to
specify conf.hpretype
Added missing comment
Made greens function for line source real
Added comments
Added ls as an option to the imp WFS driving function
Corrected y-direction of pw for 3D NFC-HOA
Updated test_driving_functions()