Enhancing TrackStack

[markmac99]

Largely work done by @tammojan but with some work by @markmac99 to handle error conditions and simplify the code:

Adding the ability to create a trackstack filtered by shower eg -s PER, and to create a trackstack for multiple days, and to set the output folder python -m Utils.TrackStack dir1 dir2 dir3 -s showerlist -o somewhere

dir_path can be a list of folders for example different nights of a shower -s showers - optional, comma-separated list of showers e g PER,cap,ARI (case insensitive) -o somewhere - optional, save the output in a different location to avoid overwriting an existing trackstack -d optional, set blackpoint to minimum detected value (darkens sky considerably, may be undesirable for some users)

Note: shower-filtration requires the FTPdetect files and a valid .config file (default read from RMS folder). Note: tqdm is not normally installed on the pi though its deployed by anaconda on other platforms. Rather than requiring a new module, i put some logic in to use the old progress indicator if tqdm was not available.

Allows the user to create a trackstack of multiple nights for a shower, as shown in the attached Perseid extract for the nights 8-11 Aug.

[markmac99]

Tested on Windows 10 / Python 3.7.9 Pi4 / Python 3.7.3 Pi3 / Python 2.7.9