Allow restriction of crawls to a single domain

[machawk1]

This has been requested a few times but there is currently no way to do this in the WAIL interface, most recently by Beaudry Allen, Digital Archivist at Villanova.

Q: What needs to be included in a Heritrix crawl job to restrict a crawl to a single domain?

Related: #350

[machawk1]

Adding the following to a crawl configuration should accomplish this:

 <bean class="org.archive.modules.deciderules.surt.OnDomainsDecideRule">
      <property name="decision" value="ACCEPT"/>
 </bean>