class Codeception\\Module: rename assertLower/Greater methods to conform...

... to PHPUnit\\Framework\\Assert naming scheme

PHPUnit documentation consulted: http://apidoc.phpunit.de/classes/PHPUnit_Framework_Assert.html


renames:

assertGreaterThen => assertGreaterThan
assertGreaterThenOrEqual => assertGreaterThanOrEqual
assertLowerThen => assertLessThan
assertLowerThenOrEqual => assertLessThanOrEqual

(retain deprecated backward compatibility methods)