kcms/desktopppaths: use "folder" and update tooltips

The FormData.label for the path entry fields currently calls the XDG user directories "paths", which seems unnecessarily technical and does not match the tooltip shown when hovering over the fields, which calls them "folders". In addition, the tooltips/Accessible.descriptions are sometimes overly verbose or incorrect (such as stating that changing the Desktop folder path will also move the files there, which it does not).

This change makes the labels use the term "folder", yielding simpler labels such as "Music folder" instead of "Music path", makes the tooltips more compact and informative, and adds translation contexts.

before	after