JSON serialization of RegisteredService into LDAP

Handles https://github.com/Jasig/cas/issues/681

I striped down the `DefaultLdapMapper` so the entire service definition is persisted into a single attribute as JSON. There are setters that allow extending the serializer, and I also modified the tests to adjust the objectclass required. Some classes had to include getters for serialization to properly work. 
This seems to do the job well:

```java
        String v = null;
        if (attr.isBinary()) {
            final byte[] b = attr.getBinaryValue();
            v = new String(b, Charset.forName("UTF-8"));
        } else {
            v = attr.getStringValue();
        }

        if (StringUtils.isNotBlank(v)) {
            return v;
        }
        return nullValue;
```