Fixed #432, setting multiple contenteditables.

It seems that if something else has the input focus when we call `set`
on a `contenteditable`, the wrong text is deleted. By clicking on the
`contenteditable` first, we ensure we'll delete the right text.
Better fix for #432, setting contenteditable.

deleteText was deleting the wrong text, not because the focus was
on another element, but because previously selected text was still
selected. Now we clear the selection before adding the new text to
it.
Merge pull request #433 from eostrom/master

Fixed #432, setting multiple contenteditables.