'span' elements surrounding inline blockable elements set as ephemeral.

To be able to set the caret after inline blockable elements, empty
'span' elements are added at the beginning and end of all inline
blockable elements. When saving the page these 'span' elements were
saved in the page. 
Setting the class of the 'span' elements as 'aloha-ephemeral' solves
this issue, so they will be removed before saving the page.