add UNO API loadStylesFromDocument

avoid opening again a document that is already available
apply to calc - refactoring ScStyleFamiliesObj::loadStylesFromURL

Change-Id: I6b26c91265dcafa73b472bc68ee684ba0733b0ac
Reviewed-on: https://gerrit.libreoffice.org/10214
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>