AppUtils: add findResources methods

These methods provide a convenient way to discover all resources
matching certain criteria from the ImageJ application environment,
including from JAR files and from files on disk beneath the ImageJ
appliation base directory.
LUTFinder: lean on AppUtils#findResources method

The logic here has been completely generalized into AppUtils. So now all
we have to do is lean on the method and it does all the work for us.
LUTService: add findLUTs method

This method does the same thing as LUTFinder, but leans on the
new AppUtils#findResources methods to do it much more simply.
LUTFinder: deprecate in favor of LUTService
DefaultLUTService: use built-in findLUTs method

The LUTFinder is now deprecated, and the LUTService has its own findLUTs
we can use here instead.
LUTFinderTest: clean up style
LUTFinderTest: use LUTService#findLUTs instead

Of course, the class name "LUTFinderTest" is now a misnomer, so we'll
rename it in the next commit.
Rename LUTFinderTest to LUTServiceTest
MandelbrotSetImage: clean up style
MandelbrotSetImage: use LUTService#findLUTs

There is no need to use the LUTFinder class anymore.
MandelbrotSetImage: remove unnecessary overrides
LUTSelector: clean up style
LUTSelector: use LUTService#findLUTs

There is no need to use the LUTFinder class anymore.
Merge branch 'lut-discovery'

This branch generalizes the LUT discovery mechanism into a new method of
the AppUtils utility class. It is also migrates the LUTFinder#findLUTs
method into the LUTService where it belongs (so that the implementation
can be overridden like any other service method).