NumberAxis.showEndTickLabel(orientation, show)

#566: We could turn off tick labels on both sides, but we couldn't choose to only turn off ticks on a single side. This branch adds a function to change whether or not the end ticks show up on the right or left, top or bottom.

For example, on an axis with horizontal orientation (either `top` or `bottom`), you can turn on ticks only on the right with
```
axis.showEndTickLabel("right", true);
```

Close #566.
Separate the getter/setter JSDoc?