Use system proxy environment variables
Add verbose option (prints out full jarsigner command)
Check jarsigner is executable
Log proxy args and directory to be zipped. Warn about password logging.
release-webstart build target replaced with signed/unsigned targets

Removed release-webstart build target
Add release-webstart-unsigned target (doesn't sign jars)
Add release-webstart-signed target (self signs jars using omero_insight_sign.py).
release-all runs release-webstart-unsigned so the final artifacts will be unsigned.

webstart-sign target has been changed to use the omero_insight_sign.py script instead of the old jarsigner ant calls
Remove sign option from jar_update_if

This means update-version won't sign any updated webstart jars.
(Actually it didn't anyway since it was removed in commit ff99355573f0145cf9eca3bed6c345b5232eded7, this just cleans up build.xml)
Remove the remaining unused code-signing ant tasks
Allow jarsigner without args to return 0 or 1

Return code depends on Java version
Change check_jarsigner error message (since exit 0|1 is allowed)

Just in case any pedants are reading
Merge pull request #2271 from manics/more_webstart_codesigning_tweaks

Even more webstart codesigning changes