phosh: Scale monitor resolution

wl_output gives us the unscaled resolution. We need to scale that with
the currently set scale. This brings the settings menu back to the
screen and makes the favorites menu fit.

Also take the home buttons size into account and flip width and height
on rotation.

Closes: #30

src/phosh.c

@@ -601,19 +601,29 @@ void
 phosh_shell_get_usable_area (PhoshShell *self, gint *x, gint *y, gint *width, gint *height)
 {
   PhoshMonitor *monitor = NULL;
-  gint panel_height = 0;
+  PhoshShellPrivate *priv;
   gint w, h;
+  gint scale;
+
+  g_return_if_fail (PHOSH_IS_SHELL (self));
+  priv = phosh_shell_get_instance_private (self);
 
   monitor = phosh_shell_get_primary_monitor (self);
   g_return_if_fail(monitor);
 
-  w = monitor->width;
-  h = monitor->height - panel_height;
+  scale = monitor->scale ? monitor->scale : 1;
+  if (priv->rotation) {
+    w = monitor->height / scale;
+    h = monitor->width / scale - PHOSH_PANEL_HEIGHT - PHOSH_HOME_HEIGHT;
+  } else {
+    w = monitor->width / scale;
+    h = monitor->height / scale - PHOSH_PANEL_HEIGHT - PHOSH_HOME_HEIGHT;
+  }
 
   if (x)
     *x = 0;
   if (y)
-    *y = panel_height;
+    *y = PHOSH_PANEL_HEIGHT;
   if (width)
     *width = w;
   if (height)