clear loaded data after load. closes #2592
do an initial animation update immediately after model load

properly zeroes the animations. animation at zero does not necessarily
mean its sub-transforms will be at zero, which can lead to oddly-placed
animated parts (see the pumpkinseed for an example)
make sure matrix state is restored before drawing scanner blobs. closes #2590
don't reconnect the slider signal on every layout
Reset the depth mask before clearing to fix the sectorview depth rendering issues.
Apply fix to SystemView.cpp too.
Use the renderer to set depth write.
Merge remote-tracking branch 'fluffyfreak/sector_depth_patch'