HackStudio no longer has dedicated project files, so let's get rid of
the *.hsp file concept. It'll eventually produce some files again,
but they won't be the same kind of "project" files.
This moves file extension to icon mappings from compile time macros to an
INI config file (/etc/FileIconProvider.ini), so file icons can easily be
customized and extended :^)
I also switched the format from a static file extension (".foo") to
glob-like patterns ("*.foo", using StringUtils::matches()), which allows
us to assign icons to specific exactly matching file names, like many
IDEs do - e.g. "CMakeLists.txt" or ".prettierrc".
