First implementation of route steps plugin.

1) Created plugin in Osmand/Plugins/Osmand-RouteSteps.
2) Registered plugin in OsmandPlugin.java - InitPlugin()
3) Added dialog to view all route dots in ContextMenu.
4) Save status of user selection.
5) Save changes to gpx file.


Known issues:
GPXUtilities.writeGpxFile() somehow doesn't save extentions so user selection are not being saved to gpx file.
Переименовать везде !
Плагин - RoutePointsNavigation! и соответственно классы и объекты такие (никаких RouteSteps - это не корректно)