ClassUtils: improve javadoc of loadClass methods
ClassUtilsTest: remove needless static modifier
ClassUtils: add method to get element's array type

Unfortunately, the implementation is rather hacky, but it works.
ClassUtilsTest: add test for getArrayClass
ClassUtils: make loadClass handle simple names

It is now possible to reference primitive types, java.lang.Strings as
"string", and N-dimensional arrays of anything using square brackets.

This syntax will be useful for scripts in ImageJ so that they can
declare input and output parameters in a more simple way.

Some examples:
  * ClassUtils.loadClass("char")
  * ClassUtils.loadClass("char[][]")
  * ClassUtils.loadClass("string")
  * ClassUtils.loadClass("string[]")
ClassUtilsTest: add test for loadClass(String)

In particular, there are checks for the various primitive
and array syntaxes as well as the string class shortcut.