Support CustomCommands

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>