[FIX] web_editor: remove some defaults in text edition

* On firefox, you had to click twice on a link to be able to start
typing text
* When selecting text which contained a <br/>, you were not able to
replacing it correctly (you had to click again before starting typing)
* When replacing a whole paragraph content which was below a title,
the text was not replaced and you had to click again and the title
transformed into a paragraph.
* ...