Fixing pixelated artifacts around the edges of outlined text in Java 7.

This is caused by a combination of the way we draw a pixel outline and the overlapping of the edges of antialiased text in Java 7 (seems fine in Java 6). Pushing the outline drawing down into platform specific classes so that the antialiasing can be toggled for Java.
Making sure all of the TextLayouts implement the new outline() method.

All of the TextLayout implementations are now extending AbstractTextLayout. Moved the bits that are specific to Java and iOS into "PaddedTextLayout".
Formatting.
Moved text outline fix from TextLayout to Canvas.

Turned off antialiasing in the default font context for Java 7.