add app loading splash screen and AppConfig (#279)

* add PyLoader class

* create global loader during app creation time and remove it when pyscript loading operations are done

* make the loader global and open/close when apps is starting. Also add concept of app config so users can set if they want to autoclose the loader of handle it themselves

* add pyconfig file

* auto add global config if there's no config set in the page

* remove changes to simple_clock example

pyscriptjs/src/components/pyloader.ts

@@ -0,0 +1,38 @@
+import { BaseEvalElement } from './base';
+
+export class PyLoader extends BaseEvalElement {
+    shadow: ShadowRoot;
+    wrapper: HTMLElement;
+    theme: string;
+    widths: Array<string>;
+    label: string;
+    mount_name: string;
+    details: HTMLElement;
+    operation: HTMLElement;
+    constructor() {
+        super();
+    }
+
+    connectedCallback() {
+        this.innerHTML = `<div id="pyscript_loading_splash" class="fixed top-0 left-0 right-0 bottom-0 w-full h-screen z-50 overflow-hidden bg-gray-600 opacity-75 flex flex-col items-center justify-center">
+        <div class="smooth spinner"></div>
+        <div id="pyscript-loading-label" class="label">
+          <div id="pyscript-operation-details">
+          </div>
+        </div>
+      </div>`;
+        this.mount_name = this.id.split('-').join('_');
+        this.operation = document.getElementById('pyscript-operation');
+        this.details = document.getElementById('pyscript-operation-details');
+    }
+
+    log(msg: string){
+        const newLog = document.createElement('p');
+        newLog.innerText = msg;
+        this.details.appendChild(newLog);
+    }
+
+    close() {
+        this.remove();
+    }
+}