formio: Form Builder (CSS) height and scrollbar by media queries

[bobslee]

With different screen resolutions sometimes the view with the Form Builder gets a scrollbar (on the iframe).
Maybe it's due to the iframe resizing issue, see issue: #20

The CSS media queries (file path below) ain't appropriate or optimized for all screen resolutions.

Module file: formio/static/src/css/formio_builder.css

Actions:

1. Ensure screens (devices) to be tested, eg BrowserStack service
2. Fix, change and test
3. Test on every (important) device.

[bobslee]

Done for v 16.0

Commit: 68318d7