Add jscript signing support

[tresf]

Comodo AV blocks our scripts, this is an attempt to white-list them by adding authenticode signing as a signature block at the bottom of the JScript files. This PR also adds authenticode to the .exe launcher.

This patch is only valid for 2.0 versions. These JScript files have been removed beginning with 2.1.

Thanks to the kind work of @ebourg at ebourg/jsign#69.

[tresf]

Checking the release notes for jsign 3.0:

Jsign now requires Java 8 or higher

Unfortunately, the 2.0 branch can't use Java 8, so we can't use this feature. That's of little consequence though for the following reasons:

• Comodo AV still blocks our scripts even when they're signed
• The 2.1 branch DOES use Java 8, so it can benefit from the newer jsign version

Slightly unrelated, but this PR does add support for a signed qz-tray.exe launcher, which both 2.0 and 2.1 branches could benefit from. Opening new issue to track that here: #593.

Edit: Sorry, had accidentally posted in the wrong bug report. Corrected.