Add logging function and fix various issues

[avjui]

Here some fixes that work for me.
It would be nice someone else could test it.

• add Logger.py to easily debug and get infos
• fix problems with get covers from mediaserver (always to '/mnt' in front of path)
• fix problems JPGPathFinder (sometimes there are no 'groups' after re.search)
• change method to get online cover (for some reasons sometimes i get a 'Forbidden'
• fix crash with Radio Paradise plugin

Thanks

Issues:

• Crash on Volumio Buster with Radio Paradise plugin #8
• Typo in ScrollSpecsFirstRoun'd' #7

[Maschine2501]

@avjui Hi! This seems to be a lot of effort you put in it!
I was not able to mention it or react to it due to health issues.
Since i updated some thing to get nr1-ui running with the newest buster realesase i was very busy, i will test your pull request sometime in the next weeks and give feedback :)
Thank you <3