Even more webstart codesigning changes

The commit logs should explain everything, main points:
* If `http_proxy` and/or `https_proxy` environment variables are defined they will be converted into the form required by Java when signing with timestamping
* Removed `release-webstart`, add `release-webstart-unsigned` (no signing) and `release-webstart-signed` (self signed). `release-all` calls `release-webstart-unsigned`
* Removed all existing jarsigning code, everything is done using `omero_insight_sign.py` (so `update-version` won't sign, since there's no way for it to know whether it should or not)

Possibly for discussion:
* `omero_insight_sign.py` sits under `docs/hudson` but is called from `build.xml`
* `docs/hudson/OMERO.sh` calls `release-all` to created unsigned artifacts, then signs the zip with `omero_insight_sign.py`. I could add a `release-all-signed` target instead to sign the jars in `dist/lib/insight` before zipping but this would mean we're not following the release signing workflow so closely.

Since most of the original PRs were done in a rush this should probably have a proper review- I've created a dummy PR at https://github.com/manics/openmicroscopy/pull/2 which I think includes all changes (#2069 #2088 #2193 #2241 ... unless I've missed one).