Answers should be trimmed of whitespace before evaluation

Problem/Motivation

An answer should not be rejected because of invisible whitespace; this can be very confusing and increase the chance that humans do not get the correct answer.

Probably separately, i think there also should be an option to strip punctuation. I can work on both of these if that is of interest.

Proposed resolution

Trim leading and trailing whitespace from the captcha response (the same as is done for captcha solutions!) before comparing to captcha solutions. Simply adding this at say line 93 of riddler.module:

  $captcha_response = trim($captcha_response);

Remaining tasks

User interface changes

API changes

Data model changes