FASTTool v1.4

Updates:

- FASTTool main window has an option to change air density
- Pitch control design:
>> Includes option to add 2nd order notch filter
>> GM and PM are now indicated in the bode plot as well as their values
>> Added -180 and 180 degrees lines in the phase plot
- AeroDyn version of FAST library is now updated to version 15.04