Added support for taking a snaspshot of a CanvasImage.

On iOS in particular, this can substantially improve performance if you will be
rendering the snapshot into other canvas images many times. This is also useful
on iOS if you just plan to render an Image into a Canvas many times, because
iOS will (I believe only in low memory situations) re-decode the image from its
PNG source data every time you draw it which is very slow. So you can render
the Image into a CanvasImage and then snapshot that CanvasImage to get maximum
"render into Canvas" performance out of your image, at the cost of forcing the
OS to keep the uncompressed image data (for that image) in memory.

This is not yet implemented for HTML and Flash. TODO!
Oops, missed an import.
Patch from Radek that clears out references in destroyed bodies.

This makes it less likely that if a game hangs onto a reference to a destroyed
body, it will end up retaining a huge graph of bodies.
Use swizzling.
Destroy test layers when removing them.
Disable fancy logging in tests. It's peskily verbose.
Added a mechanism for making getImageSync work on HTML.

It's somewhat hacky in that it just preconfigures the width and height based on
a preloaded image manifest (which the app can provide however it wants). But
it's simple and it does what is needed for most apps that just want to be able
to immediately make size decisions after loading an image. The rest of the
rendering pipeline takes care not to freak out about not-yet-loaded images.
Report our type and bufferId in toString().
Enable/disable audio in onWindowFocusChanged.

Some Android devices/versions of Android will resume your app when the screen
is turned on even if it's still showing the lock screen. In theory
onWindowFocusChanged is only called when your app is *actually* made visible
again. Yay for shit an app developer shouldn't have to care about.
Check for errors after a prepare-induced flush().
Adding support for HiDPI mode.

There are probably still issues, but things mostly work so we'll commit this to
history and go from here.
Adding tests-html to SBT build, wiring up superdevmode.
Clear the current test when going back to the menu.
Specify scale factor to HTML test with ?scale=X.
Configuration -> Config. Verbosity--.
Note to self: add some non-square-images to test suite.
Don't publish test projects.

I should extract this from the POM as well...
Account for scale factor when we draw an image into a canvas.
Added HtmlGraphics.registerFontMetrics for overriding font line height.

Font measurement in HTML5 is a giant hack, and it's not super surprising that
browsers return wildly different values for the height of a line of text. This
allows a game to override the measured values and just use a value that is
consistent and will actually result in sanely rendered text across browsers.
Prune unused imports.