Add muted and playsinline attributes (#2124)

Fixes: #2099

To be able to add videos to sites that behave as GIFs, two attributes are needed for the videos to be properly handled on iOS and in Chrome: muted and playsinline.

Muted
Chrome only allows videos to autoplay when the contain the muted attribute. Non-muted videos will not autoplay unless the user has interacted with the site. More details here:  https://developers.google.com/web/updates/2017/09/autoplay-policy-changes#new-behaviors

Playsinline
The playsinline attribute allows developers to specify videos on iPhone should play inline and not automatically enter fullscreen mode when playback begins. More details here: https://developers.google.com/web/updates/2017/09/autoplay-policy-changes#new-behaviors

system/src/Grav/Common/Page/Medium/VideoMedium.php

@@ -94,6 +94,40 @@ public function autoplay($status = false)
         return $this;
     }
 
+    /**
+     * Allows to set the playsinline attribute
+     *
+     * @param bool $status
+     * @return $this
+     */
+    public function playsinline($status = false)
+    {
+        if($status) {
+            $this->attributes['playsinline'] = true;
+        } else {
+            unset($this->attributes['playsinline']);
+        }
+
+        return $this;
+    }
+
+    /**
+     * Allows to set the muted attribute
+     *
+     * @param bool $status
+     * @return $this
+     */
+    public function muted($status = false)
+    {
+        if($status) {
+            $this->attributes['muted'] = true;
+        } else {
+            unset($this->attributes['muted']);
+        }
+
+        return $this;
+    }
+
     /**
      * Reset medium.
      *