Provide check logic as service

With this release, the check logic has been moved to the service class ChallengeResponseService. The service as well as the included JavaScript can therefore now be used to prevent automated spambot submissions for other forms in TYPO3 (e.g. extbase forms).

Changelog:

[FEATURE] Move check logic to service #33
[FEATURE] Implement additional obfuscation method strrev #35