Update minimal window dimensions

Some day we'll probably lower these minimums but first we'd need a more
responsive design.

Fixes #310

// FREEBIE

js/panel_controller.js

@@ -68,8 +68,8 @@
                 focused: true,
                 width: 580,
                 height: 440,
-                minWidth: 230,
-                minHeight: 150
+                minWidth: 600,
+                minHeight: 360
             }, function (windowInfo) {
                 inboxWindowId = windowInfo.id;
                 appWindow = windowInfo;