[GREENFOOT-856] GF installer associates GF with too many file types

Under Linux Mint (currently 20, but the behaviour has been observed for years), the Greenfoot installer seems to associate Greenfoot with many file types that it should leave alone. The extremely annoying consequence is that every time I click on a file of type ".txt" or ".bluej", Greenfoot launches and tries to open the file.

Issue metadata

Issue type: Bug
Priority: Medium