Updated Linux walkthroughs for OMERO 5.0.5

Corresponds to https://github.com/manics/omero-install/commit/0a21fde81d644f4cf8054018fc65796529b23056

Note nginx setup has been changed to make it easier to test Apache too (though theses scripts haven't been included in this PR)
Update doc to take account of the changed Nginx installation order
Refer to the server optimising pages intead of the glossary
Fix wording of section reference
Merge pull request #1009 from manics/rebased/develop/linux_walkthrough-5.0.5

Update Linux walkthrough to 5.0.5 (rebased onto develop)