engine: Add header to each response.

- This patch adds headers to each response with the option
  of defining extra headers in the web.xml. There are 3
  headers added by default.
  - X-FRAME-OPTIONS: SAMEORIGIN (To stop click jacking)
  - X-CONTENT-TYPE-OPTIONS: NOSNIFF (To stop mime type attacks)
  - X-XSS-PROTECTION: 1; MODE=BLOCK (To enable IE XSS filter)

Change-Id: I4e9c26dddd0d0300d6b3d078ae763b78600f25d1
Signed-off-by: Alexander Wels <awels@redhat.com>