This commits deletes all references and code for back-bdb and back-hdb.
There is some follow up work still necessary to flush out the admin
guide for back-mdb.

Also replace BDB example with LMDB

Move ldapi into $(RUNDIR)/run/openldap

(which was axed log ago)

Add additional comments.
Trim modules

privs, additive/substractive rules, and rule continuation.  Existing
rules that use 'defaultaccess none' should be 100% compatible.  Rules
that rely other defaultaccess settings will require addition of
explicit clauses granting the access.
Needs additional testing and tuning of logs

Set defaultaccess to 'read' in distribution slapd.conf and add warnings
Set schemacheck to 'on' in distribution slapd.conf and add warnings