Refactor create new drawing

[tim-kilian]

Problem

As I could figure out, how to create a new drawing I created a new instance for it and used a setTimeout hack. This is not the right way and should be refactored. Maybe loading a new drawing should be part of the lib.

renew-ui/src/components/header/menu/dropdowns/MenuDropdownFile.vue

Lines 78 to 91 in 571043b

	newDrawing () {
	this.$instances.modeler = new Modeler();
	this.$instances.modeler.addFormalism(PluginBase);
	this.$instances.modeler.addFormalism(PluginPT);
	this.$instances.simulator = new Simulator();
	this.$instances.simulator.addFormalism(PluginBase);
	this.$instances.simulator.addFormalism(PluginPT);
	this.$store.commit('setActiveContext');
	setTimeout(() => {
	this.$store.commit('setActiveContext', contexts.modeling);
	}, 0);
	},
	open: function () {