Put in controls and framework for window pos pref

Did not add the preference class yet, so it won't load from file; this is
next.  Will need to implement signaling to indicate whether the
preferences have finished initializing yet.
Add preferences backend, implement window pos'n

Add SetListPrefs.lvclass, which works towards #22.  Implements a
preference system that is saved to disk in an xml file when the quit
button is pressed, and loaded at startup.  There are VIs available to
force sections to wait until initiliazation of the preferences from disk
is done, allowing you to act on startup from values stored on disk.

Used this system to implement storing a preferred window position that
will automatically be returned to on startup. (If desired).
Add pref. to hide devices in "Add Device" menu

Added preference item to SetListPrefs.lvclass, interface on the
Preferences pane, and the action to the actual menu internals.

Now AddDevice.vi looks up devices by name instead of menu index, but I
left the old functionality in place under a Disable structure, so if this
breaks behavior I wasn't aware of it should be pretty staightforward to
switch it out.

Addresses #22.
Removed local prefs from repo, added to .gitignore

I accidentally checked in my local copy of SetListPrefs.xml.  This commit
removes it and adds the file to .gitignore to keep myself and others from
doing this again.
Added pref & implementation to Auto-Update HW

Accomplished by replacing every property node that changed the "Update
HWI" button to the enabled state to a conditional that either does that or
sends a signaling change value to true event to trigger the update.
Add/implement "Detach Variable Manager @ Startup"

More of the same.  Used a global tucked into VMUI.vi to pick between the
Attach & Detach on VMUI initialization.  Also put a hold on initializing
until after the pref system has finished reading from file.

Addresses #22.