SubVI structure for Prepare/Finalize; Closes #43

All children of Device now MUST override 4 subVIs (ParseSWI,
RequestTrig, Prune, BuildHWI) instead of Prepare and Finlalize. This
provides clearer structure to the job of "updating HWI" from table in an
effort to make sharing trigger lines safe.

Devices which were already complete (DDS, NI card, Novatech) still
override Prepare and Finalize and only include "stubs" of the four
above. However, to give future programmers a good example, at least one
of these ought to be copied over to the new subVI paradigm.
Remove duplicate Slave_Line class

This class was put into DeviceVIs\TestDevices and no longer needs to be
here too.
Include "isRampable?" with Column class

ConfigFunc.vi ("SetFunc") now includes a flag called "isRampable?". This
is used to say whether you intended to pass this columns data through
RampGenerate and is used to determine if Preview Cell... should be
shown. This could also be used in the future to address the ambiguity
discussed in #42.