examples: widgets.rs: new material_icons_font_ttf usage
examples: widgets.rs: new material_icons_font_ttf usage

* use new material_icons_font_ttf
* introduce new Glyphs: "MD_*" to elements

Signed-off-by: Ralf Zerres <a55c5beace021459791f5070a9a90148cd697b8f@networkx.de>

redox-os/orbtk