added initial rdata implementation for DynECT

DynECT records have an internal `rdata` map that corresponds to the fields in Master binary format in DNS.  

This is an initial implementation which shows RData as subtypes of `Map<String, Object>` with domain-specific accessors.  Note: values are often `UnsignedInteger` as in DNS, usually numbers are unsigned 32-bit numbers.

ex. NS is pretty simple
```
import static org.jclouds.dynect.v3.domain.rdata.NSData.nsdata;
...
record =  Record.<NSData> builder()
                   .zone("egg.org")
                   .fqdn("egg.org")
                   .id(50959331)
                   .type("NS")
                   .ttl(86400)
                   .rdata(nsdata("ns4.p28.dynect.net."))
                   .build();

nsdname = record.getRdata().getNsdname()
```
while SOA is (the most) complicated

```
record =  SOARecord.builder()
                      .zone("adrianc.zone.dynecttest.jclouds.org")
                      .fqdn("adrianc.zone.dynecttest.jclouds.org")
                      .id(50976579l)
                      .type("SOA")
                      .ttl(3600)
                      .serialStyle(INCREMENT) // note this is not in Record
                      .rdata(SOAData.builder()
                                             .mname("ns1.p28.dynect.net.")
                                             .rname("contact.jclouds.org.")
                                             .serial(1)
                                             .refresh(3600)
                                             .retry(600)
                                             .expire(604800)
                                             .minimum(60).build()).build();

UnsignedInteger serial = record.getRdata().getSerial();
```