Add e-mail sending testing command

[ywarnier]

Add a command to send an example e-mail through the Chamilo e-mail system.
This would allow making sure that Chamilo can effectively send e-mails (which would avoid many doubts while finishing an installation).
Ideally, there would be a few options, like giving the destination and the type of e-mail (welcome mail, global announcement mail, password reminder mail, etc).

This is just a "nice to have"

[ywarnier]

One important element would be the possibility to display possible errors happening while sending the e-mail