Reading and writing disk files.

Able to successfully write user data to disk, retrieve it from disk,
modify, re-save, and re-retrieve it.

-	Wrote my own serialization process.  Uses NSJSONSerialization to read
and write.  Wrote an extension to NSDictionary which lets me convert my
objects to and from JSON in one line of code per property, instead of
(say) iterating through lists of data and converting individual
properties and array contents.  Note that the open-source project
JSONModel probably does this more scalably (although I haven’t tried
it), but I had already started down the path of doing it myself.

-	I added two data classes:
	-	LMUConfigurationDatabase:  contains 0…n configurations
	-	LMUDataManager:  handles opening and saving files, and tracks the
current Configuration being shown in the main view controller.  This
probably isn’t the right way to do this, but it’s clean, simple, and
accurate for now.

-	The list of data classes is now:
	-	LightFixture:  an actual lamp.  One of the things we’re selling.
	-	LightFixtureType:  defines the type ID and available colors for the
different lamp types.
	-	FixtureGroup:  a cluster of lamps that are electrically turned on
and off together.
	-	Configuration:  a cluster of FixtureGroups and/or ungrouped
LightFixtures.
	-	ConfigurationDatabase:  a bunch of Configurations, exactly one of
which the user is currently editing.  Wraps a single JSON file.  This
is the top-level element in the JSON files I’m reading and writing.
	-	DataManager:  opens and saves files.  Maintains pointers to the
currently-open Database and to the Configuration currently being
modified by the user.

-	We now have two main data files:
	-	the user’s data file, stored in the user-data directory
	-	a file defining the available Fixture Types.  Currently in
FixtureTypes.json, bundled with the app.

-	And we have these views:
	-	CurrentConfiguration: the list of lamps and groups that the user is
editing.  This is currently the main view, the thing the user sees when
the app starts.
	-	FixtureEditor:  lets the user define a lamp and its type
	-	Several “color editors,” each a ViewController, which let the user
modify the output of a specific lamp:  ColorPicker (for the
red/green/blue/white lamps), WarmNeutralCool (for the
warm/neutral/cool-light lamps), and UltraVioletColorPicker (for the UV
lamps).