client: add area measurement. simpify code * Add a third draw mode which can only be activated when no morphology is selected and we are already in LineString mode. It adds an area calculation. Because the Polygon drawMode ends on a double click, there needs to be an extra callback for this to run identify so that the area calculation is shown all times. * Add Bernhard as author to some files and also simplify copyright note. * Remove DRAWMODES in the code to simplify as this is just one indirection used once in stores/application.js. * Use mapState instead mapGetters to get the drawMode at all places to save some code lines.