Add Soot dependency from the "definitive" build server

[bechang]

This is a trial in using the Soot "central" build server.

[bechang]

@ftc So what I found is that you have use https to reference the build server now. I don't know, but perhaps you could use http in the past.

[bechang]

On my machine, I ran into an SSL certificate error:

Server access Error: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target url=https://soot-build.cs.uni-paderborn.de/nightly/soot/soot-trunk.jar

I had to resolve it by grabbing the certificate from Firefox and then importing into manually into the Java keystore. This seems really yucky, but it looks like it worked fine on Travis. We should find out if this is an issue for others before we merge.

[bechang]

To resolve the SSL certificate here, I used a combination of these two pages:

• https://stackoverflow.com/questions/21076179/pkix-path-building-failed-and-unable-to-find-valid-certification-path-to-requ
• https://blog.alwold.com/2011/06/30/how-to-trust-a-certificate-in-java-on-mac-os-x/

Very sketchy, but it was all that I could find.

[jpw234]

Works on my machine

[octalsrc]

Compiles and tests successfully for me

[smover]

It works on mac

[jpw234]

I'm alright with at least attempting to keep up with their nightly build for the moment, so I'll approve this PR