Blender Git Loki

Make window-level scene switching work

Add some comments about methods used for mass-spring model

Set better default values for the new mass-spring model

Implement bending springs along shear springs within polygons

This adds bending springs within polygons, so that they resist
changing planarity.

Implement shear springs for ngons

Initial implementation of angular bending springs

This implements bending resistant forces between adjacent polygons in
cloth simulation. Note that derivatives are not yet included in the
computations (and might not even be needed, as the simulation is already
quite stable). Angular damping is not yet implemented either.

Update RNA and UI scripts to use scene from window

Main work to move active scene into window

Added scene as argument to area/region listeners. It's only used in a really few cases though, I might instead do a lookup.

fix for constraint calculation, transform of meshisland centroid was calculated incorrectly

Unittest scene copy

Unitest: doversion, write and read test for layers

Merge branch 'master' into cycles_split_kernel

Cycles: Keep consistent memory management style

`unique_ptr` avoids some issues but we aren't using it anywhere else so
to keep things consistent just using plain `delete` for now.

Cycles: Make split kernel methods in Device private

These methods shouldn't really be called from anywhere except
`DeviceSplitKernel`.

Cycles: Remove overloaded Device::mem_alloc function

It was a bit confusing having two versions of this function, only one is
needed really. Added `device_memory::resize()` to take over the behavior
the overload provided.

Revert "Experimental Cycles Build"

This reverts commit 90ba99d99b5512c14f52afc3e29668980c48e5dc.

Experimental Cycles Build

This build contains:

- Denoising
- Light Groups
- Shadowcatcher
- Blue-Noise Dithered Sampling
- Custom Scrambling distance
- IES lights
- Disney BSDF
- Highlight Compression

Merge remote-tracking branch 'origin/master' into experimental-build

Cycles: Ensure we get a compiler error if data_init parameters fall out of sync

Code isn't so pretty and the errors that we get if this does happen are kind
of cryptic, but it's better than nothing.

Add cent_poly_v3 function