fix #10024 - Add an option in Preferences/Look-and-Feel to use native file-choosing dialogs.
They look nicer but they do not support file filters, so we cannot use them (yet) as default.
Based on patch by Lesath and code review by simon04.
The native dialogs are not used if selection mode is not supported ("files and directories" on all platforms, "directories" on systems other than OS X)

git-svn-id: https://josm.openstreetmap.de/svn/trunk@7578 0c6e7542-c601-0410-84e7-c038aed88b3b
see #10529 - fix mapcss unit test

git-svn-id: https://josm.openstreetmap.de/svn/trunk@7579 0c6e7542-c601-0410-84e7-c038aed88b3b
fix #7166 - include second and milliseconds in filename of autosaved deleted layers to avoid potential name collision

git-svn-id: https://josm.openstreetmap.de/svn/trunk@7580 0c6e7542-c601-0410-84e7-c038aed88b3b
applied #10546 - mapstyle: prioritize natural tags over sport tags (patch by Klumbumbus)


git-svn-id: https://josm.openstreetmap.de/svn/trunk@7581 0c6e7542-c601-0410-84e7-c038aed88b3b
remove "external source" warnings for plugins hosted on https://github.com/JOSM

git-svn-id: https://josm.openstreetmap.de/svn/trunk@7582 0c6e7542-c601-0410-84e7-c038aed88b3b