Add hover help to most element of the admin interface

[benoitg]

This is an ISF priority. Mechanic already pratially implemented by fproulx, but may not yet fill the entire use case. There has to be a way to display large blocks of structured text. Either through preformatted text (ideal for translation) or html markup.

[max-horvath]

I'd suggest not to have it as a hover help but like a button next to each item which when being clicked will show an help area ...