examples/CMakeLists.txt: Rename NOM_BUILD_GUI_EXAMPLES var

NOM_BUILD_GUI_EXAMPLES -> NOM_BUILD_GUI_EXAMPLE

* This completes the intended splitting up of the gui examples.
Convert old tests to use GTest framework

	The test files have been converted and original source removed:
tests/graphics-tests.cpp -> tests/graphics/RenderWindowTest.cpp
tests/math-tests.cpp -> tests/graphics/MathTest.cpp
tests/system-tests.cpp -> tests/system/FileInterfaceTest.cpp

	Related files removed:
* tests/Makefile
* tests/run.sh

* tests/CMakeLists.txt: Use TESTS_DEPS_INSTALL_PREFIX cmake var
for the destination path when copying resources.
* tests/CMakeLists.txt: Remove redundant NOM_BUILD checks for
initial setting of individual unit tests; these checks are
done before inclusion of a test.

* tests/CMakeLists.txt: Only copy JSON, XML, font resources when the
appropriate unit tests are being built.

* tests/CMakeLists.txt: Fix compile err with operator ++ and
operator -- method overloads.
Fix compile errs in cursors & macros example

* Correct the usage of NOM_DUMP to NOM_DUMP_VAR; these changes were
forgotten about when we swapped the API of NOM_DUMP_VAR and NOM_DUMP,
in a commit from yesterday.