Split Code-Mutator functionality

We need to separate the mutators for genericode codelists and simple text/value based codes, since the latter one can have more functionality.

acceptance criteria

• genericode editor is available via name "genericode" (explicit) -> CodeMutator is renamed to GenericCodeMutator
• the simple value is availabel via names "text", "value" and "code". This is done in #94, being combined with the old TexMutator
• implementation overlap is reduced