Add processors to remove POST data and cookies

[ste93cry]

In the Ruby Raven client two processors that remove cookies and POST data from the request before submitting the event to the server have been added in getsentry/sentry-ruby#252 and getsentry/sentry-ruby#445. However, it seems that the PHP client is not maintained as much as the other and so it still leaks possible sensitive informations. The PR I submitted should fix the issue in the same way as the PR getsentry/sentry-ruby#466. Please note that I took the opportunity to move the processors to a new directory and I deprecated the old Raven_SanitizeDataProcessor class: it should be removed in the next major version.