This content has three sections - two of which are shown on a different
level which looks rather awkward.
Move content to setup LDAP server in separate file and reference it
properly.
Fix also a wrong headline markup and indent.
Rename identity-secure-identity-to-ldap-backend.rst to
identity-secure-ldap-backend.rst. Adjust htaccess for that.
Change-Id: I1a822304f1232211cc32f1b4553417dc2ccfeb45
c5728e0ebf