Text uses a global FontManager
Text vertical aligment also include h and y for reference

If we don't do this, vertical alignment only depends on the
characters that happen to be in the string, leading to
inconsistent vertical alignment, and subsequently to jumpy
spacing between pieces of text that should be equally-spaced.
Text allows global manager, but not by default.
Merge pull request #455 from almarklein/text-share-manager

Text uses a global FontManager