preservationmeter: Fix for invalid extension.

* If unknown or invalid extension then the score returns 0.

Signed-off-by: Joao Goncalves <jsvgoncalves@gmail.com>
preservationmeter: Adds cfg for quality mapping.

Signed-off-by: Joao Goncalves <jsvgoncalves@gmail.com>
preservationmeter: Adds and improves testing.

* Adds a singleton class for Record mocking.
* Improves overall tests.

Signed-off-by: Joao Goncalves <jsvgoncalves@gmail.com>