Map paint settings: wrong file filter for adding local style files

[Cobra]

The "open file" dialog for adding a local map paint style shows only *.gpx, *.osm, *.nmea, *.jpg, ... files instead of style files (*.mapcss, *.xml). There is no other option like "all files", so it's quite difficult to select a local file: the only way is typing the whole file name.

[bastiK]

In 5572/josm:

fixed #8184 - Map paint settings: wrong file filter for adding local style files

[stoecker]

@bastiK:

Zip is missing.

[bastiK]

In 5576/josm:

add *.zip to FileFilter (closes #8184)