Right-to-left labels support

Added right to left  word ordering support for the label core and the
label widget. Used for hebrew, arabic etc. to resolve incorrect word
ordering (and resulting line breaks) when rendering RTL text.
Essentially, we scan the words in reverse order (to ensure proper ordering of 'split' lines in case the label has a width constraint and is rendered over several lines), and reverse the glyphs to handle the reversed ordering of letters in these languages. Tested using hebrew and english.