Update to generator-webapp guidelines

I tried to mirror some changes from the supreme master generator, including:

- Renamed `all` to `app`, so you can invoke the generator by just typing `yo ember`
- Fixed grunt build, which failed due to jshint errors before
- Added `main` attribute to package.json
- Made test framework configurable
- Renamed `Generator` to `EmberGenerator`
- Removed executable bits from files
- Updated jshint
- Various style fixes
- Utilize `generator.installDependencies()`
- Show Yeoman ASCII Art!