Support for single Canvas rendering (OpenGL Canvas accelerators)

Original discussion in the mailing list: https://groups.google.com/forum/#!msg/limejs/7URDfYUhX1w/t682EkGPgcgJ

First target is to support Ejecta https://github.com/phoboslab/Ejecta , but it should be mostly compatible with others as well. Pull requests are welcome to support other platforms.

**Work in progress. Report issues you have with your own games or if this breaks current behavior in any way.**

### Testing:

```
git fetch origin
git checkout no-dom
```

#### In the browser:

See and tweak:

- lime/demos/tests/run_canvasonly.htm
- lime/demos/roundball/rb2.html
- lime/demos/zlizer/zlizer2.html

#### Ejecta

You need a Mac/Xcode for this. To test on a real device you have to be registered iOS developer.

Clone Ejecta from https://github.com/phoboslab/Ejecta

```
cd path/to/lime
EJECTA_ROUNDBALL=path/to/ejecta make ejecta-roundball
EJECTA_ZLIZER=path/to/ejecta make ejecta-zlizer
```

To build both games you currently need two clones of Ejecta on different paths. This command will build it for simulator. To run on a device open the Ejecta project after simulator build, select your device and hit run.