Avoid errors if olm is missing

If olm isn't installed, webpack prints out scary warnings (though it still
actually succeeds). Let's avoid scaring people by quietly removing it from the
list of things to process.

webpack.config.js

@@ -102,3 +102,12 @@ module.exports = {
     ],
     devtool: 'source-map'
 };
+
+// olm is an optional dependency. Ignore it if it's not installed, to avoid a
+// scary-looking error.
+try {
+    require('olm');
+} catch (e) {
+    console.log("Olm is not installed; not shipping it");
+    delete(module.exports.entry["olm"]);
+}