Including public cookie methods

Adding to the Mink module the methods "see/don't see cookie" and "grab cookie".
Fixing _getCookie()

_getCookie() wasn't returning anything.
Including set and reset cookie methods

Adding ways to alter cookies to improve tests that depends on cookies.
Adding tests for new cookie methods and fixing a typo in a random test's name
Merge pull request #329 from igorsantos07/patch-1

Including public cookie methods