Various logging cleanups

* don't just log errors without any context as to where they came from or what
   they mean
 * avoid the use of '%s' and multi-argument console.log because it looks awful
   under karma.

src/components/structures/MatrixChat.js

@@ -330,7 +330,7 @@ module.exports = React.createClass({
                     defaultDeviceDisplayName: this.props.defaultDeviceDisplayName,
                 });
             }).catch((e) => {
-                console.error("Unable to load session", e);
+                console.error(`Error attempting to load session from token params: ${e}`);
                 return false;
             }).then((loadedSession) => {
                 if (!loadedSession) {