Add LdapAuthenticationHandler based on ldaptive.

Unit tests require the following environment/devleoper-specific files to
exist in the module root directory:

 1. ldaptive.properties
 2. credentials.properties
 3. extraConfigContext.xml

There are sample versions of each file for reference.
Factor out authnConnectionConfig bean.

Allows supporting use cases such as custom truststore configuration.
Merge branch 'feature-new-authn-api-ldaptive' of github.com:serac/cas into feature-new-authn-api-ldaptive

Conflicts:
	cas-server-support-ldap/extraConfigContext.xml.sample
	cas-server-support-ldap/src/test/resources/applicationContext-test.xml