add open on last.fm button

public/index.html

@@ -73,6 +73,7 @@
 				<li><a class="ctx-item" data-action="queue">Queue Track</a></li>
 				<li><a class="ctx-item" data-action="edit">Edit Metadata</a></li>
 				<li><a class="ctx-item" data-action="download">Download</a></li>
+				<li><a class="ctx-item" data-action="lastfm">View on Last.fm</a></li>
 				<li class="ctx-multi"><a class="ctx-item playlist-add" style="display: none;">Add to Playlist</a>
 					<ul class="ctx-sub-items playlist-list" id="ctx-playlists"></ul>
 				</li>

public/index.js

@@ -294,6 +294,18 @@
     })
   }
 
+  function lfmurl (i) {
+    return i.replace(/\s/g, '+')
+  }
+
+  function popLastFMPage (tid) {
+    httpGet('/api/track/' + tid).then(function (metadata) {
+      window.open('https://www.last.fm/music/' + lfmurl(metadata.artist) + '/_/' + lfmurl(metadata.title))
+    }, function (e) {
+      console.log(e)
+    })
+  }
+
   function ctxHandle (el) {
     if (ctxState === 0) return
     let dt = el.getAttribute("data-action")
@@ -310,6 +322,9 @@
       case 'download':
         window.open('/api/serve/by-id/' + ctxState + '?dl=1', '_blank')
         break
+      case 'lastfm':
+        popLastFMPage(ctxState)
+        break
       case 'edit':
         editTrack(ctxState)
         break