Created Calibrator class

This class ensures that all the cameras have been calibrated. It manages
the camera events related to calibration and communicates with the PSO
system to calculate camera positions. This appears to be completed.
PSO System

The files for the PSO system used to calculate camera positions. These
are from the Tracer-Bullet, but have been tweaked for readability and
integration into the Sketchup system.
Added Line class

Added a class to wrap the data for a line (i.e. a point (vec3) and a
line (vec3)). Used by the ModelConstructor.
Replaced ConstructionBlock with InputBlock

Replaced ConstructionBlock with InputBlock (which is more politically
correct). Also added a timestamp, which is used by the ModelConstructor
to invalidate expired camera events.