Fix label plugin

[timothymtorres]

So while I was overhauling the plugin system I noticed something. The label plugin has many of the variables referenced incorrectly.

Not just that the map.extension property is not even used in Map:extend. I’ll fix them, but it may take me a day or two.

[timothymtorres]

After looking at CoronaSDK and Tiled documents I think I’m going to add text support directly to objects instead of as a plugin.