Allow "space" to pass through so that auto-correct works on Mobile Safari

if no range is selected -- and hence we are not "overwriting" a selection -- then we should allow the "space" to pass through as default rather than inserting '\u00A0'. Allowing the space to be treated default makes auto-correct continue to work on (at least) iPhones, where the "space" event is what triggers auto-correct, auto-complete, auto-capitalization, 2 spaces marking the end of a sentence, etc. Otherwise, auto-correct breaks.

This does create one small problem, where an inserted space, as the first or only character of added text, will not trigger the "tracking" code to be added. Not sure how to handle that...