Added support for specifying sensor id and axis transform for VRPN devices to eqc files.

Added support to specify the sensor id of the tracker (there may be multiple sensors on at the same address).
The default is to gracefully find and use the lowest active sensor.
Specify vrpn_tracker_sensor as: ANY, LOWEST, or sensor id integer
Added support to specify a tracker to eq-space transformation, as either a matrix or axis string.
Specify vrpn_tracker_axis as: [[FLOAT FLOAT FLOAT][FLOAT FLOAT FLOAT][FLOAT FLOAT FLOAT]] where
each vector represents the X, Y, and Z tracker axis
Or as an axis string (regex): [XYZxyz]{3} where lowercase denotes negative, uppercase positive
E.g., These two representations are equivalent (map X to X, Y to -Z, and Z to Y):
[[1 0 0][0 0 -1][0 1 0]] == XzY
Added more debug info; now using scoped_ptr