Reversing priority of channels-slices-frames for ij.plugin.Animator's nextSlice and prevSlice commands for hyperstacks

When you have a hyperstack with multiple channels, slices and frames, the scroll wheel of the mouse in the pre-commit imagej works on the channels, and if you hold alt or control or space, then works on slices or frames.  For most users, there are probably only a few channels (2-4), but there are probably many slices or frames, or both.  The scroll wheel and the "next" or "previous" slice commands should most naturally operate on frames without any modifier key, and then on slices, and then channels.  That is, with this change, when opening a multi-dimensional hyperstack, the mouse wheel scrolls through frames, and then slices with the control key, and channels with alt or space held down.  

Just as a small issue, too, in the old one, control or space did the same thing which was change z, and alt was used for frames.  However, when you press alt in windows, it is "sticky" and makes menus pop up unless you hit it again.  Therefore if any key should have redundancy it should be alt.  So now I never have to use the alt key, instead I can use space, which is nice.

Additionally, with multi-dimensional images, I like to "animate" them through frames using "Start Animation [\]", but I would like to still be able to easily scroll through slices.  So now when you turn on animation in a stack with slices and frames (which plays the frames), the scroll wheel and next/prev slice automatically work on slices.  Before it would simply stop the animation.

These changes also work with simpler just slices and frames, or just frames and channels, etc. in an expected way.

Behavior for non-hyperstack stacks is the same.

Also I combined the nextSlice and prevSlice methods into a single jumpSlice method, with the original methods calling that one, just because it was easier to work on.  Not sure if it is better/worse to do it like that?