Improved strings in template.

Only relevant part of string will go through the Python internationalization function.

lms/templates/videoalpha.html

@@ -63,7 +63,7 @@
                         <a href="#" class="add-fullscreen" tabindex="0" title="${_('Fill browser')}">${_('Fill browser')}</a>
                         <a href="#" class="quality_control" tabindex="0" title="${_('HD')}">${_('HD')}</a>
 
-                        <a href="#" class="hide-subtitles" title="${_('Turn off captions')}">Captions</a>
+                        <a href="#" class="hide-subtitles" title="${_('Turn off captions')}">${_('Captions')}</a>
                     </div>
                 </div>
             </section>
@@ -75,12 +75,12 @@
 
 % if sources.get('main'):
     <div class="video-sources">
-        <p>${_('Download video <a href="%s">here</a>.') % sources.get('main')}</p>
+        <p>${(_('Download video') + ' <a href="%s">' + _('here') + '</a>.') % sources.get('main')}</p>
     </div>
 % endif
 
 % if track:
     <div class="video-tracks">
-        <p>${_('Download subtitles <a href="%s">here</a>.') % track}</p>
+        <p>${(_('Download subtitles') + ' <a href="%s">' + _('here') + '</a>.') % track}</p>
     </div>
 % endif