Make the fixed navbar optional

Adds another on/off preference (default: on, keeps same
behaviour) for the fixed navbar.
When off the navbar will not remain at the top of the
page when scrolling.
This is useful for small displays such as phones where
otherwise the navbar takes up a sizeable portion of
the viewport.

templates/settings.html

@@ -59,6 +59,11 @@
 				<input type="hidden" value="off" name="autoplay_videos">
 				<input type="checkbox" name="autoplay_videos" {% if prefs.autoplay_videos == "on" %}checked{% endif %}>
 			</div>
+			<div id="fixed_navbar">
+				<label for="fixed_navbar">Keep navbar fixed</label>
+				<input type="hidden" value="off" name="fixed_navbar">
+				<input type="checkbox" name="fixed_navbar" {% if prefs.fixed_navbar == "on" %}checked{% endif %}>
+			</div>
 			<div id="use_hls">
 				<label for="use_hls">Use HLS for videos
 					<details id="feeds">