Add default picture to device (Fixes #39)

Uses a '?' as the default picture for devices in case child classes don't
implement their own.  Decided to leave the thrown error if picture not
found as this is an actual error that needs to be fixed, and there is not
appropriate error indicator to connect the VI. The user has the option to
press continue and ignore the problem, so it won't prevent the use of
SetList even if the PNG file somehow gets deleted.

Fixes #39.
Slave-slave conflict gives chan.# in error message

To help user find problems, the error message now include channel number
information instead of just stating there was a collision.  Fixes #40.
Update default Trigger Channel to 65535. Fixes #38

Changes the default trigger channel to 65535 (Max unsigned 16-bit value)
for new devices to help make errorneously unprogrammed trigger channels
obvious.
Master requires Check_Reserved_Lines override

Because this is part of our device collision error checking routine, we
require all master devices to implement the Check_Reserved_Lines VI.

Fixes #45
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.
Merge pull request #46 from CHerold/Fixes-Held-for-Freeze

Fixes held for freeze; other work finished so freeze is over.
quiet Slave error dialog

wired error w/o branch.
Also added missing novatech init error wire.
Merge branch 'master' into Add-Menu-Column