[C2] Health check box on admin page

[ywarnier]

Some issues on a new Chamilo portal can be difficult to diagnose if they are stemming from a bad configuration.

I think we should add a block on the admin page called "Health check" (as many other software do) and show a few indicators there, starting with whether all settings required for e-mail sending are effectively configured.

The block would just show a list of items (<ul> list) with a green check or a red cross if not properly configured, and a link to configure them properly.

For example,

• if the mail DSN or the origin sender e-mail are not defined, it should say so and link to /admin/settings/mail (text: "E-mail settings are OK")
• if there are more than one active URL and the global admin is not in all of them, it should point to /main/admin/access_url_edit_users_to_url.php (text: "Admin has access to all URLs")