Zero out roll when stopOrientation is called (fixes #1230).

Previously, all the internal calls to `stopOrientation` were followed by
setting the roll to zero, but this was not done when the function was called
via the API. As this roll parameter is only used for device orientation
control, there's no API method to change it, so it was previously not possible
to zero out the roll when device orientation control was stopped using
the API.

src/js/pannellum.js

@@ -803,7 +803,6 @@ function onDocumentMouseDown(event) {
     stopAnimation();
 
     stopOrientation();
-    config.roll = 0;
 
     speed.hfov = 0;
 
@@ -932,7 +931,6 @@ function onDocumentTouchStart(event) {
     stopAnimation();
 
     stopOrientation();
-    config.roll = 0;
 
     speed.hfov = 0;
 
@@ -1181,7 +1179,6 @@ function onDocumentKeyPress(event) {
     latestInteraction = Date.now();
 
     stopOrientation();
-    config.roll = 0;
 
     // Record key pressed
     var keynumber = event.which || event.keycode;
@@ -2569,6 +2566,7 @@ function stopOrientation() {
     window.removeEventListener('deviceorientation', orientationListener);
     controls.orientation.classList.remove('pnlm-orientation-button-active');
     orientation = false;
+    config.roll = 0;
 }
 
 /**