A series of small bug fixes and improvements to the C++ code

[jeremykubica]

Fixes a series of small bugs and memory inefficiencies in ImageStack and TrajectoryList including:

• Incorrect bounds checking for index bounds
• Inadvertent copy during sort (by not passing references)

Adds a move constructor (and an explicit copy constructor) to LayeredImage

Also enhances ImageStack by:

• Adds the ability to set or append images (so we don't need to copy a full vector)
• Saves a local copy of width and height to simplify bounds checking code.
• Updates height and width when inserting the first image into a stack.