feat(DCOS-13976): Disable opening the UI in iframe
feat(DCOS-13976): Disable opening the UI in iframe

This PR adds X-Frame-Options to prevent Clickjacking attack through iframe.

surdy/dcos,lingmann/dcos,GoelDeepak/dcos,mellenburg/dcos,mesosphere-mergebot/dcos,lingmann/dcos,vishnu2kmohan/dcos,lingmann/dcos,kensipe/dcos,surdy/dcos,mellenburg/dcos,BenWhitehead/dcos,branden/dcos,asridharan/dcos,amitaekbote/dcos,mellenburg/dcos,surdy/dcos,kensipe/dcos,dcos/dcos,dcos/dcos,amitaekbote/dcos,dcos/dcos,BenWhitehead/dcos,surdy/dcos,GoelDeepak/dcos,BenWhitehead/dcos,asridharan/dcos,BenWhitehead/dcos,kensipe/dcos,lingmann/dcos,mesosphere-mergebot/dcos,mesosphere-mergebot/dcos,GoelDeepak/dcos,amitaekbote/dcos,dcos/dcos,mesosphere-mergebot/mergebot-test-dcos,vishnu2kmohan/dcos,branden/dcos,amitaekbote/dcos,dcos/dcos,mesosphere-mergebot/dcos,mellenburg/dcos,mesosphere-mergebot/mergebot-test-dcos,vishnu2kmohan/dcos,vishnu2kmohan/dcos,branden/dcos,mesosphere-mergebot/mergebot-test-dcos,branden/dcos,asridharan/dcos,asridharan/dcos,kensipe/dcos,mesosphere-mergebot/mergebot-test-dcos,GoelDeepak/dcos