UbuntuShape should be available as an image provider

We use UbuntuShape extensively everywhere in the Ubuntu UI. In a *lot* of places, it just means masking the image and adding the borders. Doing this every time you load the image feels wasteful, and is causing slowdowns in the UI (e.g. dash).

I think we should also have the ability to use an image provider that will fetch the image, apply the shaping and flatten the image, allowing for caching (on disk as well) the resulting image.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-ui-toolkit-doc 0.1.46+14.04.20140408.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
NonfreeKernelModules: wl nvidia
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Apr 23 12:58:14 2014
PackageArchitecture: all
SourcePackage: ubuntu-ui-toolkit
UpgradeStatus: No upgrade log present (probably fresh install)