Add xterm itegration

* Move to TypeScript from legacy JavaScript
* Add support of xterm.js
* Hterm is still available for backward compatibility

js/dist/xterm.d.ts

@@ -0,0 +1,24 @@
+import * as bare from "xterm";
+export declare class TermXterm {
+    elem: HTMLElement;
+    message: HTMLElement;
+    messageTimeout: number;
+    messageTimer: number;
+    term: bare;
+    resizeListener: () => void;
+    constructor(elem: HTMLElement);
+    info(): {
+        columns: number;
+        rows: number;
+    };
+    output(data: string): void;
+    showMessage(message: string, timeout: number): void;
+    removeMessage(): void;
+    setWindowTitle(title: string): void;
+    setPreferences(value: object): void;
+    onInput(callback: (input: string) => void): void;
+    onResize(callback: (colmuns: number, rows: number) => void): void;
+    deactivate(): void;
+    reset(): void;
+    close(): void;
+}