added population data back for SIMPLE_CHILD_ARRAY implementation
moved blended _children union into BLENDED_UNION_CHILDREN
clean up voxel server stats page
added SIMPLE_EXTERNAL_CHILDREN mode, which saves on most of our child VoxelNode children storage without being too complicated
add mutex for _nodesRequestingJurisdictions to fix crash
Merge pull request #1139 from ZappoMan/voxelnode_memory_savings

VoxelNode memory savings
Merge pull request #1138 from ZappoMan/bugfixes

add mutex for _nodesRequestingJurisdictions to fix crash
flip mirror tools
Merge pull request #1140 from ZappoMan/bugfixes

flip mirror tools
Rear view zoom level

new zoom icons
save and restore state from settings
display zoomed out rear view when selected
Merge branch 'master' of https://github.com/worklist/hifi into 19447

Conflicts:
	interface/src/ui/RearMirrorTools.cpp
fix packetData memory leak in AvatarMixer
add debug to catch AvatarMixer ghosting
remove the ground plane
Starfield fix and Milky Way

Fixed bug where more stars were generated at the poles.

Added 'Milky Way' band in sky, customisable with MILKY_WAY_WIDTH,
MILKY_WAY_INCLINATION and MILKY_WAY_RATIO consts in Generator.cpp.
add debug for sleep amount to AvatarMixer
Merge pull request #1143 from birarda/assignment

add node kill debugging, remove ground plane
made sending environments off by default
Merge pull request #1144 from ZappoMan/stephens_requests

made sending environments off by default
have silent node removal flag reset on join