Fix and simplify options settings, making -b and -l work.

* Removed environment ENTENTE_* settings to use popt arguments only.
Removed the #define BASEDN and made it use the -b option. Fixed the -l
option so it correctly binds to all ports when -l is not provided.

* Updated entente.defaults and entente.init.d to use options settings.
Added ENABLE=0 support so it can be disabled.

* Updated README.md to remove references to the removed ENTENTE_*
environment settings.