code cleanup in ImageResource

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6160 0c6e7542-c601-0410-84e7-c038aed88b3b
see #8849 - add `emergency=phone` and `emergency=aed` to internal preset.
TODO: update map paint style to use scaled down version of .svg

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6161 0c6e7542-c601-0410-84e7-c038aed88b3b
applied #8987 - immutable coordinates (patch by shinigami)


git-svn-id: http://josm.openstreetmap.de/svn/trunk@6162 0c6e7542-c601-0410-84e7-c038aed88b3b