Merge pull request #3 from mholden8/master

Modified to use transform buffers to store trajectories.
Fixes #5: Outlined improvements to user interface are implemented.
Moved module to "Perk Tutor" category.
Fixes #7: Added option to trace out paths of tool trajectories. Added option to copy metrics from the metrics table to clipboard.
Fixes #8: Playback snaps to message when double-clicked. Refresh widget only when the transform buffer is modified, instead of every 10ms.
Added functionality to calculate user-configurable metrics defined in python scripts.