Refactor per event views into a generic show view event

Instead of wrapping the 'navigate' method call with multiple 'show' events, we want call the 'navigate' method from a single event.

So, instead of...

this.on('*:showService', this.navigate_to_service);
this.on('*:showUnit', this.navigate_to_unit);
this.on('*:showCharm', this.navigate_to_charm);
this.on('*:showEnvironment', this.navigate_to_environment);

... we will have...

this.on('*:navigateTo', function(e) {
 console.log('navigateTo', e);
 this.navigate(e.url);
}, this);