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 pull request #787 from manics/rebased/develop/codesigning_doc

Add code-signing documentation (rebased onto develop)
Remove repetition of the word "files"

This removes repetitive use of "files" in one of the limitations.txt headers.
Merge pull request #792 from bpindelski/rebased/develop/patch-2

Remove repetition of the word "files" (rebased onto develop)