Provide option that deactivates text modifications

[matze-dd]

In order to suppress rare, but annoying false positives from the proofreading software, we have included special macros like \LTadd and \LTskip, as well as 'magic' comments.

It might be reassuring to have a CLI option that deactivates all these changes to the input text. For instance, \LTadd would add nothing, and \LTskip would copy its argument to the plain text sent to the proofreader.