Distance field text rendering

[DaneGardner]

Right now we're just generating a texture map for each text object, and pasting that onto a scaled rectangle. This works fine for some zoom levels, but doesn't do well when at either extreme of zooming (in or out). A week after implementing the text rendering methods for this library Nokia announced new methods for Qt5. We should look at the code and possible incorporate these methods so we don't have to upgrade to Qt5 yet. See this link for more details: http://labs.qt.nokia.com/2011/07/15/text-rendering-in-the-qml-scene-graph/