* Add custom license header style in order to comply with Google's Checkstyle format
* Update license headers to comply with Google's Checkstyle format
* 1) Test cases were not stopping AudioService before ending test case 2) Changed Audio to be a good singleton, previously because of Audio being bad singleton, test cases which were using static methods could have caused intermittent failures. 3) Made some other refactorings as well
* Removed sonar issue and converted Audio to eager singleton for simplicity
* Updated class diagram PNG
When the system is not capable to play the sound, do not throw
exception, just log it. For example on Linux there are several issues to
play sound and there are no workarounds for that :(
