Do not insert BR in empty inline elements when parent node contains text

This solves the bug shown in the gif...
![bold_space_bug](https://cloud.githubusercontent.com/assets/5630563/4476796/cfeb79be-4978-11e4-926d-6d06e9eeecc4.gif)

and the fix....
![bold_space_fix](https://cloud.githubusercontent.com/assets/5630563/4476805/e6011a88-4978-11e4-9227-946fc5a7397b.gif)


I think it might be better if we'd use `!isBlockElement` in _scribe-common_. That way we should cover all types of elements, and also custom elements (which are inline by default).