Resources (#1)

* start some resource fiddling

* start some resource fiddling

* initiate a real resource manager

* fix color flicker in rendering

* delete unintended constructors

and add a convenience function to reset the render-image (from the
original image, aka. clone again)

* [OpenGL deprecation warning]

The compiler said that these functions are "deprecated". They seem to
be useless anyway...

* various improvements

* add resource enumerator and documentation

* fix constness stuff

* use existing iterator for insertion

* init unit tests

* rm bogus file

---------

Co-authored-by: m-aXimilian <keuffnermax@gmail.com>

tests/CMakeLists.txt

@@ -0,0 +1,19 @@
+include(${PROJECT_SOURCE_DIR}/modules/googletest.cmake)
+
+add_executable(libpixelarium_UnitTests
+  lib/resources/test_resource.cpp)
+
+target_include_directories(libpixelarium_UnitTests
+  PUBLIC ${PROJECT_SOURCE_DIR}/lib
+  PUBLIC ${OpenCV_INCLUDE_DIRS}
+)
+
+
+target_link_libraries(libpixelarium_UnitTests
+  pixelariumresourcelib
+  pixelariumimagelib
+  GTest::gtest_main
+  GTest::gmock)
+
+include(GoogleTest)
+gtest_discover_tests(libpixelarium_UnitTests)