Ldap.txt: cleanup and update column names.

This change goes in hand with the PR fixing #2587. It updates
the description of the logic used for LDAP user lookup and mentions
the new column in the "experimenter" table.
merge develop -Dorg -Ijburel/openmicroscopy:qa-submit-new -Ssuccess-only: PR 990 (for users who have compiled isapi_wsgi on x64)
merge develop -Dorg -Ijburel/openmicroscopy:qa-submit-new -Ssuccess-only: PR 1014 (Ldap.txt: cleanup and update column names.)
merge develop -Dorg -Ijburel/openmicroscopy:qa-submit-new -Ssuccess-only

Repository: openmicroscopy/ome-documentation
Already up-to-date.

Merged PRs:
  # PR 990 kennethgillen 'for users who have compiled isapi_wsgi on x64'
  # PR 1014 bpindelski 'Ldap.txt: cleanup and update column names.'

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