Enable declarative configuration of pyramid_ldap connection and searches

In this series I enable "out of the box" configuration of the ldap searches
via the pserve .ini file.

I've been forced to change the replacement strings from traditional %(key)s style
to string.Template style to stop pserve from trying to expand them at startup time.

While I like the shell-like ${key} syntax, I'm not going to die for it if you would
prefer for me to update to str.format's {key} syntax.

Thank you very much,

   l.