Multiple paths for YAML files and FixtureSets

[h4cc]

As requested in https://github.com/h4cc/AliceDemo/issues/4 it would be a nice feature if fixture files and sets could be loaded from other or even multiple paths.

The current implementation using that single hardcoded path might not suite everywhere-

My idea is to have a list of paths relative to bundle base path configured somehow somewhere, which can also be changed by configuration.