create prune simulator

A stand-alone ExtJS app that allows experimenting with different backup
schedules and prune parameters.

The HTML for the documentation was taken from the PBS docs and adapted to the
context of the simulator.

For performance reasons, the week table does not use
subcomponents, but raw HTML.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

docs/prune-simulator/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
+    <title>PBS Prune Simulator</title>
+
+    <link rel="stylesheet" type="text/css" href="extjs/theme-crisp/resources/theme-crisp-all.css">
+    <script type="text/javascript" src="extjs/ext-all.js"></script>
+    <script type="text/javascript" src="prune-simulator.js"></script>
+</head>
+<body></body>
+</html>