Fix greyscale image handling

Fix image handling (img_crop, normalize_and_crop, load_scaled_image_arr) to deal with greyscale images correctly.
Also various spelling fixes.

Enable throttle scaling while controlling manual throttle

Allow PWM freq. of PCA9685 to be specified

Update create_application.md

Update setup_jetson_nano.md

Update MakeMovie to allow plotting of user data only (no model) - useful for determining quality of user input.
Also fix the confusing mix of model argument being None vs "None".

Also includes code to scale PWM values appropriately based on the freq. specified.

mentioned the ~/mycar directory in the myconfig.py section

* Use index to correctly go from first to last frame
* Use index from tub instead of try/catching on continuous frames
* Use picture frame size to determine mid of and length of user / pilot line plots
* Remove unused code/variables
* Some pep-8 formatting

Fix PartProfiler showing wrong number for KerasLinear

Fix PartProfiler to take KeyboardInterrupts into account as well as initialisations of parts. It seems like on_part_finished() is not called when a KeyboardInterrupt occurs leaving the time value in the time difference which messes up the timing table max and avg values. Here, we simply chop off first and last entry form the timing arrays. We also add a median to the table to see if the distribution of timings is skewed.