Support displaying layer list in outliner

Adds a new outliner display mode "Layers" in which the basic layer tree is drawn. The button for restricting layer visibility is also already there.

Fix crash when deleting active layer

Merge branch 'master' into soc-2016-layer_manager

Conflicts:
source/blender/blenloader/intern/versioning_270.c
source/blender/editors/interface/resources.c

Quiet compiler warning

Merge branch 'master' into soc-2016-layer_manager

Merge branch 'master' into soc-2016-layer_manager

Conflicts:
source/blender/blenkernel/BKE_blender_version.h

Change to object mode when hiding layer of edit object

Merge branch 'master' into soc-2016-layer_manager

Conflicts:
source/blender/blenkernel/intern/depsgraph.c
source/blender/blenkernel/intern/object_dupli.c
source/blender/blenloader/intern/versioning_270.c
source/blender/modifiers/intern/MOD_cloth.c
source/blender/modifiers/intern/MOD_dynamicpaint.c
source/blender/modifiers/intern/MOD_smoke.c

Make scene copying work with layers

Use utility for adding new object layer tree when adding new scene

Missed this in last commit.

Add utility for adding new object layer tree with default layer

Merge branch 'master' into soc-2016-layer_manager

Fix crash deleting objects

Initially add visibility bits as layer property

As decided in T38384, this adds the visibility bits as layer property for testing.
Each layer now has the 20 visibility bits that are compared to the ones from the object. The viewport header shows the bits of the active layer.

The bits currently only affect drawing.

Found & removed some more Scene.base usages

Also NULL the Base.next/prev pointers after version patching

Deprecate Base.next/prev pointers

For now we won't use them, but we might go back to storing bases in lists again to avoid trouble with file read/write. However, these lists will still work different than the current base list.

Add/use macro for circular base iterations

Refactor base iterators to be much simpler

Make use of the new BKE_objectlayer_base_first_find and BKE_objectlayer_base_next_find functions, instead of doing some cryptic, nested loop stuff.

Optimize base lookups by storing index in bases

Add helper functions to find last and next base in object layers