Add ability to remove morph targets from mesh

[tlf30]

This PR adds the ability to remove MorphTargets from Mesh.
It also adds a helper function to get a single MorphTarget.

~Trevor

[Ali-RS]

Note that if a mesh has no MorphTargets, then the morphTargets field will be null, and thus calling each of those newly added methods will throw NPE.

Maybe we should better to check if it is null then:

in case of boolean removeMorphTarget(MorphTarget target) return false
in case of MorphTarget removeMorphTarget(int index) throw IndexOutOfBoundsException
in case of MorphTarget getMorphTarget(int index) throw IndexOutOfBoundsException

Any thoughts?

[stephengold]

My thoughts: avoid throwing NPE in these methods. Getter and index-based remove method should throw IndexOutOfBoundsException. Instance-based remove method should return false.

[pspeed42]

If you have to pass an index in and the index is out of bounds then you should throw an index out of bounds exception. What sgold says. :)

[tlf30]

I had not considered when there are no morphs, I will update the PR when I get home tonight. As it stands a index out of bounds will get thrown when the index it out of range when not null.

[tlf30]

I have made the requested changes.

[Ali-RS]

Looks fine to me, thanks.

[Ali-RS]

If no objection, I am going to merge this in the next 24 hours.