OO-2060 prevent calling of context menu on video elements

src/main/java/org/olat/modules/video/ui/_content/video_preview.html

 <div class="o_video_run o_block_large_bottom o_clearfix">
 	<div class="olatFlashMovieViewer">
-		<video id="$r.getId("o_vid")" width="$width" height="$height" controls  autoplay class="o_video">			
+		<video id="$r.getId("o_vid")" width="$width" height="$height" controls  autoplay preload="none" oncontextmenu="return false;" class="o_video">			
 	    	<source type="video/mp4" src="$mediaUrl/$filename" />
 		</video>
 

src/main/java/org/olat/modules/video/ui/_content/video_run.html

 <div class="o_video_run o_block_large_bottom o_clearfix">
 	<div class="olatFlashMovieViewer">
-		<video id="$r.getId("o_vid")" width="$width" height="$height" poster="$masterUrl/poster.jpg" controls  preload="none" #if( $autoplay ) autoplay #end class="o_video">			
+		<video id="$r.getId("o_vid")" width="$width" height="$height" poster="$masterUrl/poster.jpg" controls  preload="none" oncontextmenu="return false;" #if( $autoplay ) autoplay #end class="o_video">			
 	    	#foreach($video in $videos)
 	    		#set($position = $velocityCount - 1)
 	    		<source type="video/mp4" src="$transcodedUrl/${video.getResolution()}video.mp4" title="$displayTitles.get($position) ($r.formatBytes(${video.getSize()}))" />