Add support for Trac-report like Jira-report

This is the new feature for making a HTML report of Trac tickets like jira-report.
Trac-report needs Trac-XMLRPC-Plugin in Trac.http://trac-hacks.org/wiki/XmlRpcPlugin
The Trac must use basic authentication.
This patch adds following goal:
changes:trac-report

To use this function, for example:

[pom.xml]
...
<issueManagement>
<!-- system must be "trac" -->
<system>trac</system>
<!-- Trac URL with Trac-XMLRPC-Plugin -->
<url>http://localhost/trac/SampleProject/</url>
</issueManagement>
...
<reporting>
<plugins>
<!-- changes-plugin -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-changes-plugin</artifactId>
<version>2.0-beta-3</version>
<configuration>
<!-- tracUser permited trac XMLRPC-plugin -->
<tracUser>admin</tracUser>
<tracPassword>admin</tracPassword>
<!-- query condition (If this property is "null", all tickets are reported) -->
<query>status!=closed&owner=admin&order=type</query>
<!-- encoding -->
<outputEncoding>Windows-31J</outputEncoding>
</configuration>
</plugin>
</plugins>
<reporting>
...

To generate report from above pom.xml:

$ mvn site

Report is generated at target/site/trac-report.html.

About Trac, refer to the official site.:http://trac.edgewall.org/