fix display of notifications when the map is not displayed

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6339 0c6e7542-c601-0410-84e7-c038aed88b3b
refactor of some GUI/widgets classes (impacts some plugins):
- `gui.BookmarkList` moves to `gui.download` as it is only meant to be used by `gui.download.BookmarkSelection`
- `tools.UrlLabel` moves to `gui.widgets`
- `gui.JMultilineLabel`, `gui.MultiplitLayout`, `gui.MultiSplitPane` move to `gui.widgets`



git-svn-id: http://josm.openstreetmap.de/svn/trunk@6340 0c6e7542-c601-0410-84e7-c038aed88b3b