Add event-handling feature to the Map

[hergert]

The API should expose the functionality to add an event to the Map instance in the following way:

            var map = new mapTools({
                id: 'mymap',
                lat: 41.3833,
                lng: 2.1833,
                on: {
                    'zoom_changed': function(e){/**/};
                }

map.on('zoom_changed', function(){});