Support for Galileo

[emiedmee]

I've been working with the Quectel RM500Q-GL module, which has a GNSS engine and can output NMEA sentences.
I found your project and it almost fit my needs, except that I'm not using GLONASS but a combination of GPS and Galileo.
So I've decided to add Galileo support next to GPS and GLONASS in your project.
This has been tested with several files containing various states of NMEA sentences and all issues, including issues in the original code, should be fixed with PR #8 .
I've also made all the code comply more with Python coding guidlines using linters, etc.

I hope you like my work!

[nabelekt]

Hey, @emiedmee. Thanks for you contributions. I don't use this code any more (moved away from NMEA for my project), but will try to pull your branches soon and test them out. If things look good, I'll probably go ahead and merge. Thanks!

[emiedmee]

Thanks!
When testing 'add-galileo' it might be possible you run into issues when exporting to the database, because I had some issues there. That's the reason why I made the other PR.
So you might want to merge both branches first to test the database part or use my master branch (where I merged them already)