TrackChanges disrupt conversion into japanese characters

problem:

inserting japanese characters eg via Anthy does not work when TrackChanges are on.

solution：

• use rangy's getBookmark() instead of rangy's saveSelection()
• replace invisible characters only bw. two INS-Tags (= where they cause problems), not in general

additional note for Windows10:

Results are different in Windows10 than e.g. in Ubuntu, but entering japanese characters in TrackChanges on Windows10 behaves exactly the same as in other software (e.g. Notepad++ or Word).
Tested for: Firefox Quantum 62.0b14, Microsoft Edge 42.17134.1.0, IE 11.165, Google Chrome 68.0.3440.84