Login attempts

This is my proposal to solve #960

- Created failed_attempts and last_failed fields in table users.

- Only thing I changed is that If 2 > failed attempts < 5, user must wait 1 minute until next attempt instead of show captcha.

- Not really sure if this is the way to invalidate token for quick login:
https://github.com/oliverds/openclassifieds2/commit/48dd7ceef79241604389b1b10ccc17ac21c8794e#diff-c6ad5ed15188378f347bfc13fabeecd2R87