NEXUS-6569: NEXUS-5023: Fixes for std headers

Moving the IE one from ContentServlet to standard ones,
removing/replacing the misnamed header
NEXUS-6569: Few more places

removing the spread use of this header, now that
it's set at one place and applied to all
NEXUS-6569: Fix UT

I forgot to update UT when fixed the headers
Merge pull request #529 from sonatype/NEXUS-6569-std-headers-part2

NEXUS-6569: NEXUS-5023: Fixes for std headers