Cleanup tags and small change to tagging-interface

[jowouters]

In order to add multiple tags to a list, these tags have to be separated by spaces.
Although this is clearly indicated in the interface, a lot of mistakes are made. Some ppl (myself included) added tags separated by commas.

Examples:
https://privacyscore.org/browse/?tags=de,
https://privacyscore.org/browse/?tags=virus,protection,internet

In order to solve this issue, i would propose:

1/ cleanup of the existing data
. remove all commas in those tags that end/begin with a comma
. split up tags that have a comma between words

2/ change the interface by showing example tags separated by spaces instead of separated by commas
Current interface: