4571: RTL support missing in FanChart

Partial fix, approved by bmcage.
Fully RTL text will be rendered RTL, fully LTR will be LTR.
Unfortunately, CTL (combination of the both) will still be broken.
Better fix for bug# 4571 will be researched on trunk, in gtk3.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22532 4ae1f11a-8b86-4847-b8af-ab372f36d1fd