Lockfile creates the cmdfile needed by sfh.
Add Mask class for sfh

The Mask class is meant for writing the mask files
needed for the StarFISH sfh program. Currently the
Mask class just creates blank mask files. Updates
will allows masks to be edited against polygon
selections.

Includes a plot_cmd_mask() method for plotting the mask.

Note: the coordinates associated with the mask vectors
are not packed properly yet. Might require an extra flip;
test against the plot_cmd_mask() with the reshaped coordinate
vectors being plotted.