Dumped AD stuff, dumped other stuff, implemented account search

This version allows to search for LDAP accounts instead of building
the DN by the WP user name. This way, an arbitrary LDAP attribute
can be used to store the WP user name. Also, multiple WP accounts
can authenticate using the same LDAP account.

I should probably clean this patch up and create a PR against
Simple LDAP Login - of course, with the dumped stuff not dumped.