Signing warning when installing the plugin via Eclipse Marketplace

[ultraq]

Just something I noticed when testing plugin installation for #78 was that it comes up with a signing warning. It's probably to do with signing the JARs or something like that, but it might be nice to try clear that up.

I tried a few other plugins and it seems the warning is pretty normal for plugins that aren't coming out of big companies (although even the STS default install had one for some CloudFoundry plugins I believe), so this isn't a biggie.