Bounced light in LightUp v5

LightUp v4.2g

Fixes for this release include:

- fix for explicit camera aspect ratios set by ACT
- fixes for DAE exporter
- FBX and DAE exporters now output .png images which are more widely supported than .tga files
- incremental render skips VertexLit objects to reduce iteration times.
- improved startup times for larger models
- bug fixes

Lighting Sketchup Plugin