Mp3Info can take a string to check validity

[Romchik38]

1. Refactored static function isValidAudio:

• now this method only reads data from provided filename
• logic moved to new public static method isValid
• added try/cat block in case when file_get_contents returns false

2. New public static method isValid

• reads data from string and makes a file validity decision

3. Composer.json:

• created require-dev with phpunit
• created autoload-dev with folder tests
• created scripts with tests and phpunit to simplify run tests with one command composer tests

[wapmorgan]

Should remove composer.lock

[Romchik38]

Done