SA shares packages with core BEAST classes

[tgvaughan]

Historically it seems that this was the done thing, but it can easily lead to problems due to the way that all classes loaded by BEAST have to share the same namespace. If someone else adds a class to their BEAST add-on that happens to have the same name (and be in the same package) as one of yours then BEAST will refuse to load either one of the add-ons. The simple fix is to move all of your packages into a root package which you have good reason to believe is unique (at least within the BEAST world) - something like sampledancestor should do it.