Update launcher icon generator to material design

This change updates the launcher icon generator to produce material design style assets, updating existing background shape stencils (square, circle) and providing two new ones (vertical rectangle, horizontal rectangle). It also adds an additional "effects" option (long shadow, score, dog-ear).

**Things to note:**

- The icon anatomy as set out in the material design spec is not fully supported - edge tint and shadow, foreground elevation and lighting subtleties are missing.
- The long shadow effect is rendered at the target densities and not the native foreground density, because my algorithm apparently runs in O(Chrome has become unresponsive dialog) time. The gradient is also linear, not radial.
- The score effect does not add any detail along the score edge.
- The dog-ear effect is achieved through additional background stencils, not code. It supports the top-right corner of angular shapes only.
- There is no PSD for the background stencils (sorry).
- The resources zip output now places assets in `mipmap-` folders.
- The Lollipop [wallpaper background image](https://docs.google.com/uc?export=download&id=0B328pHcnJU0QaVhOQnNqR3A1NDg) I'm using is currently hosted in my Google Drive. You will probably want to update it with your own.