Replaced fest-assert-core with assertj-core

AssertJ is a fork of FEST, which itself doesn't seem to be maintained anymore.
Merge pull request #651 from Turbo87/assertj

Replaced fest-assert-core with assertj-core
Intercept HttpServletResponseWrapper#setStatus(int, String) to fix response status tracking
Merge pull request #652 from noslowerdna/filterFix

Intercept HttpServletResponseWrapper#setStatus(int, String) to fix response status tracking