Typo fix in Desklet cinnamon-settings

Corrected this:

> Some desklets require the border/header to be always preset

to the following:

> Some desklets require the border/header to be always **present**

(emphasis of course not included)

Fixed in default `.py` file and in three English localizations.

**EDIT** sorry for the extra two commits; that was supposed to be a separate branch.