Relocate conflicting class files in fat jars

[chippmann]

Especially with #441 there could be cases now where classes have the same fqName from different dependencies. If that's the case, they'll override each other, and only one of them will be present in the final main.jar fat jar. Which leads to nasty bugs.

Shadow jar has a feature where classes can be relocated to a different package path if they are conflicting, and automatically update the usages: https://imperceptiblethoughts.com/shadow/configuration/relocation/#automatically-relocating-dependencies

We should take advantage of this to prevent this issue

[travisfw]

Wasn't this the whole purpose of project Jigsaw? I thought the java module system was specifically designed to solve these problems for everyone. I certainly could be wrong…