warn that in-place ln_s import can be slower

see https://trac.openmicroscopy.org.uk/ome/ticket/12217
Add code-signing docs
Add to sysadmins/whatsnew
Add note about code-signing to build-system
Fix typo, rewrite paragraph
Change insight to OMERO.insight
merge develop -D org: PR 743 (Propose redesign of OMERO and Bio-Formats 5.0 CI jobs)
merge develop -D org: PR 782 (Custom web login 11961 (rebased onto develop))
merge develop -D org: PR 783 (document new // separator in omero.fs.repo.path (rebased from dev_5_0))
merge develop -D org: PR 786 (warn that in-place ln_s can be slower for HCS (rebased from dev_5_0))
merge develop -D org: PR 787 (Add code-signing documentation (rebased onto develop))
merge develop -D org

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

Merged PRs:
  # PR 743 sbesson 'Propose redesign of OMERO and Bio-Formats 5.0 CI jobs'
  # PR 782 will-moore 'Custom web login 11961 (rebased onto develop)'
  # PR 783 mtbc 'document new // separator in omero.fs.repo.path (rebased from dev_5_0)'
  # PR 786 mtbc 'warn that in-place ln_s can be slower for HCS (rebased from dev_5_0)'
  # PR 787 manics 'Add code-signing documentation (rebased onto develop)'

Generated by OMERO-5.1-merge-push#226 (http://ci.openmicroscopy.org/job/OMERO-5.1-merge-push/226/)