[settings] add an option to sync msoffice/libreoffice tmp file

__PLEASE NOT MERGE THIS__

* add an option to sync msoffice/libreoffice tmp file
* adjust some odd-styled code
This will leaves users to be confused if there are two parts of settings where one denies the other (sometimes or often?).

Okay, I will wait until you have made a unambiguous decision for this. Once this is made, the implementation should be there in minutes.