r6981: first version of the builtin web server for Samba4

r6981: first version of the builtin web server for Samba4

This includes an embedded server side scripting system called 'esp'
(see http://www.appwebserver.org/products/esp/esp.html) and javascript
based scripting language called 'esj' (see
http://www.appwebserver.org/products/ejs/ejs.html)

The justification for including this scripting language is that it
should make it much easier to write a high quality web interface for
Samba4. The scripting language can call into any Samba4 library code
(so for example it will be able to make ldb and loadparm calls), plus
it provides easy support for forms, cookies, sessions etc.

There is still quite a bit more work to do on the web server, but
there is enough here now for people to look at and comment. I will be
committing some sample web pages that test esp functionality shortly.