This patch will get the modified customized notebookbar*.ui
files from user directory(if present) otherwise the files will be rendered
from default shared directory.

Change-Id: I9393083bc0429659039c8dd5c10541ffa6661bf7
Reviewed-on: https://gerrit.libreoffice.org/72313
Tested-by: Jenkins
Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>