ConversionUtils: remove unnecessary elses
ConversionUtils: simplify array logic
ConversionUtils: use simpler test
ConversionUtils: be consistent with comment style
ConversionUtilsTest: rename CollectionWrapper

It is now called ListWrapper since that describes more specifically what
it does.
ConversionUtilsTest: handle private fields too

The ClassUtils#getField(Class, String) method uses getDeclaredField
rather than getField to obtain the name of the field, so that private
fields can also be accessed. Of course, then no subclasses are handled,
but for the purposes of this test class, it doesn't matter.

This change also lets us stop propagating NoSuchFieldException
throughout the tests, too.
ConversionUtilsTest: fix typo
ConversionUtilsTest: use separate struct per test

This allows each test's struct to be customized according to its needs,
rather than having one combined struct accommodating the needs of all
test methods at once.
ConversionUtilsTest: test subclass of collection