Use StringBuilder instead of StringBuffer as we don't need the thread
safe behavior.

Materialize the string before returning it. I'm not very fond of having
StringBuilders in the wild.
Use a StringBuilder instead of String concatenation
Make all Javascript resource references final.

Fix #29
Make DefaultOptionsRenderer final.
Utils should be final and have a private constructor to prevent
instantiation.
Follow the JLS suggestions for modifier orders.
Remove redundant modifiers.
No need to keep a reference to the label.
If we want the getter to work, we better have the setter working.
Use StringBuilder.append(char) instead of .append(String) where
possible.

Per gripe from Martin Grigorov in
https://github.com/WiQuery/wiquery/pull/35#commitcomment-3759761 .
Merge pull request #35 from openwide-java/general-cleanup-sonarqube

General cleanup using SonarQube and proofreading the code