Support CustomCommands

[greyfairer]

Allow to add custom mongeez commands in changesets, written in Java.

For example:

<bean id="mongeez" class="org.mongeez.MongeezRunner">
    <!-- ...-->
    <property name="customCommands">
        <map>
            <entry key="test">
                <bean class="org.mongeez.examples.dao.TestMongeezCommand"/>
            </entry>
        </map>
    </property>
</bean>

public class TestMongeezCommand implements CustomMongeezCommand {
  @Override
  public void run(MongeezDao dao, Properties props) {
     dao.runScript("db.testM.insert({test:true});");
  }
}

<changeSet changeId="SMS-1353 exec bean" author="oleksii">
    <bean>test</bean>
</changeSet>