Bring back per-viewport localview. This is based on Blender 2.79.
We have a limit of 16 different local view viewports.
We are using both the numpad /, as well as the regular /.
Missing features:
* Hack to make sure lights are always visible.
* Make rendered mode with external engines to support this as well
(probably just need to support this in the RNA iterators).
* Support over 16 viewports by taking existing viewports out of local view.
The code can use a cleanup pass in the future to unify the test to see
if an object is visible (or we can use TESTBASE in more places).
Committing this for the sake of completionism. I'm going to bring this
up for review, I think we may want to revert it.
Fundamentally I'm changing the behaviour of the operator both in object
mode (acting on all selected lattice objects), as well as the edit mode
(acting on all lattices in edit mode, regardless of them having any
selected vertice).
Committed by accident (1076523b1b).
But now I need to fix building.
Note: The operator itself shouldn't have been committed because it
should operate in the world space (for the axis), not local.
I will tackle this later.
