directly include expirychecker module

[briskt]

Added

• Copied all pertinent code, configuration, and tests from silinternational/simplesamlphp-module-expirychecker.

Removed

• Removed redundant test scenarios.

Changed

• Changed the namespace on the Validator class to avoid a custom autoload.

--

Note: the first commit is mostly just copied files, and the remainder are the changes made to those files.

[briskt]

Namespace could be changed to camelCase or PascalCase to increase readability, but it's fine as is too.

I tried, but it didn't work. Maybe just needed to rename the folder as well, but I didn't want to go down that trail any further.