Load all async-{xyz} asynchronously instead of upfront during the boot process

[ibdafna]

Plotly saves on memory by lazy-loading dependencies its apps require. These generally tend to come from the dash-core-components distribution, and are retrieved using GET requests which Flask serves. WebDash currently loads all of them upfront during the boot process.

webdash/src/webdash.ts

Lines 123 to 140 in 9857988

	// Dash core components
	const dccDir = `${sitePackagesDir}dash_core_components/`;
	const dccFiles = [
	"async-plotlyjs.js",
	"async-graph.js",
	"async-markdown.js",
	"async-highlight.js",
	"async-dropdown.js",
	"async-slider.js",
	"async-datepicker.js",
	"async-upload.js",
	"dash_core_components.min.js",
	"dash_core_components-shared.js",
	];
	for (const fileName of dccFiles) {
	scriptTags.push(await this.generateScriptBlob(dccDir, fileName));
	}

It would probably make more sense to stay true to the original intention and load these asynchronously whenever an app that depends on them, requests them.