ui: set minimum window size to 800x600

A smaller window makes it for a bad experience.

main.js

@@ -23,6 +23,17 @@ const indexURL = url.format({
  */
 let jitsiMeetWindow = null;
 
+/**
+ * Options used when creating the main Jitsi Meet window.
+ */
+const jitsiMeetWindowOptions = {
+    width: 800,
+    height: 600,
+    minWidth: 800,
+    minHeight: 600,
+    titleBarStyle: 'hidden'
+};
+
 /**
  * Sets the APP object listeners.
  */
@@ -45,8 +56,7 @@ function setAPPListeners () {
  * Opens new window with index.html(Jitsi Meet is loaded in iframe there).
  */
 function createJitsiMeetWindow () {
-    jitsiMeetWindow =
-        new BrowserWindow({width: 800, height: 600, titleBarStyle: 'hidden'});
+    jitsiMeetWindow = new BrowserWindow(jitsiMeetWindowOptions);
     jitsiMeetWindow.loadURL(indexURL);
 
     jitsiMeetWindow.on("closed", () => {