FYI: Major refactoring ahead

@carshadi, just to let you know that there have been some major refactoring of SNT's Path class:
Basically in SNT 5.0 all of the archaic arrays holding every single feature of path nodes have been replaced with a single list of PathNode objects. Quick tests on the demo datasets show faster A* searches under less memory (~20-30% for both).

I am convinced that things work smoother now with pyimagej because the architecture is streamlined significantly.

The old startJoins, startJoinsPoint fields, etc. are deprecated. They _should_ still work, but if you run into issues the new equivalent methods/fields are hopefully more intuitive:

```
Path.getStartJoins -> Path.getParentPath()
Path.getStartJoinsPoint() -> Path.getBranchPoint()
Path.setStartJoin(parentPath, branchPoint) -> Path.setBranchFrom(parentPath, branchPoint)
Path.disconnectFromAll() -> Path.detachFromParent()
````

Also, `Path.createCircles()` and a bunch of other methods related to radii are no longer needed and do nothing now.