Document and rationalize custom event emitters

[Raruto]

Also start thinking how could the be replaced or consolidated within a single place (especially for global ones), as per v3.4 I found these:

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Event Emitter API:

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g3w-client/src/app/core/g3wobject.js

Line 16 in 68da69f

inherit(G3WObject, EventEmitter);

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EventHub API:

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g3w-client/src/app/core/plugin/pluginservice.js

Line 16 in 68da69f

this.vm = new Vue();

g3w-client/src/app/g3w-ol/constants.js

Line 4 in 68da69f

export const VM = new Vue();

g3w-client/src/app/gui/app/index.js

Lines 183 to 197 in 68da69f

	return new Vue({
	el: '#app',
	created() {
	// set general metods for the application as GUI.showForm etc ..
	self._setupInterface();
	// setup layout
	self._setupLayout();
	//register all services fro the application
	self._setUpServices();
	// create templateConfig
	self.templateConfig = self._createTemplateConfig();
	// listen lng change and reset datatable lng
	this.$watch(()=> ApplicationState.lng, ()=>{
	self._setDataTableLanguage();
	});

g3w-client/src/app/gui/app/index.js

Lines 886 to 892 in 68da69f

	const app = new Vue({
	el: '#app',
	...compiledTemplate,
	data: {
	messages: error_page[language]
	}
	});

g3w-client/src/app/gui/catalog/vue/catalogeventhub.js

Line 1 in 68da69f

const CatalogEventHub = new Vue();

g3w-client/src/app/gui/form/formservice.js

Line 7 in 68da69f

this.eventBus = new Vue();

g3w-client/src/app/gui/queryresults/queryresultsservice.js

Line 20 in 68da69f

const VM = new Vue();

g3w-client/src/app/gui/relations/vue/relationeventbus.js

Line 1 in 68da69f

module.exports = new Vue();

g3w-client/src/app/gui/sidebar/sidebar.js

Line 7 in 68da69f

const SIDEBAREVENTBUS = new Vue();

g3w-client/src/app/gui/vue/vue.directives.js

Line 6 in 68da69f

const vm = new Vue();