UJOTYP-5: Add hashing functionality to the variant

• add hashing function
• extend variant to cache his hash value (just calculated once and only if needed)
• add test for hashing function
• add two test tool functions with inverted logic (fails, if values match)
• add test tool function for message output
• change comparison mode of existing test tool functions for easier understanding of the source
• rename comparison functions of test tools for clearer understanding
• change error output texts and use the new message output function
• add missing source files to CMakeLists.txt
• order source files in CMakeLists.txt alphabetically