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/pyconfig.ts

@@ -0,0 +1,55 @@
+import * as jsyaml from 'js-yaml';
+import { BaseEvalElement } from './base';
+import { appConfig } from '../stores';
+
+let appConfig_;
+
+appConfig.subscribe(value => {
+    appConfig_ = value;
+});
+
+export type AppConfig = {
+    autoclose_loader: boolean;
+    name?: string;
+    version?: string;
+  };
+
+export class PyConfig extends BaseEvalElement {
+    shadow: ShadowRoot;
+    wrapper: HTMLElement;
+    theme: string;
+    widths: Array<string>;
+    label: string;
+    mount_name: string;
+    details: HTMLElement;
+    operation: HTMLElement;
+    code: string;
+    values: AppConfig;
+    constructor() {
+        super();
+    }
+
+    connectedCallback() {
+        this.code = this.innerHTML;
+        this.innerHTML = '';
+
+        this.values = jsyaml.load(this.code);
+        if (this.values === undefined){
+            this.values = {
+                autoclose_loader: true,
+            };
+        }
+        appConfig.set(this.values);
+        console.log("config set", this.values);
+    }
+
+    log(msg: string){
+        const newLog = document.createElement('p');
+        newLog.innerText = msg;
+        this.details.appendChild(newLog);
+    }
+
+    close() {
+        this.remove();
+    }
+}