build: allow to disable language support in cmake

* in addition: add unloadable sourcegroup to visualize, load and save information when loading a project that contains source groups that are not supported by the build

src/lib/settings/source_group/component/java/SourceGroupSettingsWithClasspath.cpp

@@ -1,5 +1,7 @@
 #include "SourceGroupSettingsWithClasspath.h"
 
+#if BUILD_JAVA_LANGUAGE_PACKAGE
+
 #include "ProjectSettings.h"
 #include "utility.h"
 
@@ -50,3 +52,5 @@ void SourceGroupSettingsWithClasspath::save(ConfigManager* config, const std::st
 	config->setValues(key + "/class_paths/class_path", getClasspath());
 	config->setValue(key + "/use_jre_system_library", getUseJreSystemLibrary());
 }
+
+#endif // BUILD_JAVA_LANGUAGE_PACKAGE