Resolve posterURL and torrentPath at runtime

Fixes bug where posters and torrent files can’t be found in the built
app.

renderer/util.js

@@ -0,0 +1,9 @@
+var path = require('path')
+
+var config = require('../config')
+
+exports.getAbsoluteStaticPath = function (filePath) {
+  return path.isAbsolute(filePath)
+    ? filePath
+    : path.join(config.STATIC_PATH, filePath)
+}