Document the Packager tool for both Maven2 and command line usage

Hi Xavier,

To use the packager plugin in m2 do the following:

1) Add the xwiki remote repository either to your settings or in your pom.xml file:

  <repositories>
    <repository>
      <id>xwiki</id>
      <name>XWiki Maven2 Remote Repository</name>
      <url>http://maven.xwiki.org</url>
      <releases>
        <enabled>true</enabled>
      </releases>
    </repository>
  </repositories>

2) Then follow the sample located at http://tinyurl.com/yd22mg

This examples uses default locations but you can control the parameters using the following plugin configuration elements:

For import:

    /**
     * @parameter default-value = "xwiki"
     * @see com.xpn.xwiki.tool.backup.Importer#importDocuments(java.io.File,String,java.io.File)
     */
    private String databaseName;

    /**
     * @parameter default-value = "${basedir}/src/main/packager/hibernate.cfg.xml"
     * @see com.xpn.xwiki.tool.backup.Importer#importDocuments(java.io.File,String,java.io.File)
     */
    private File hibernateConfig;

    /**
     * @parameter default-value = "${basedir}/src/main/documents"
     * @see com.xpn.xwiki.tool.backup.Importer#importDocuments(java.io.File,String,java.io.File)
     */
    private File sourceDirectory;

Here's the javadoc for the parameters:

     * @param sourceDirectory the directory where the package.xml file is located and where the
     *        documents to import are located
     * @param databaseName some database name (TODO: find out what this name is really)
     * @param hibernateConfig the Hibernate config fill containing the database definition (JDBC
     *        driver, username and password, etc)

And for export:

    /**
     * @parameter default-value = "xwiki"
     * @see com.xpn.xwiki.tool.backup.Exporter#exportDocuments(java.io.File, String, java.io.File)
     */
    private String databaseName;

    /**
     * @parameter default-value = "${basedir}/src/main/packager/hibernate.cfg.xml"
     * @see com.xpn.xwiki.tool.backup.Exporter#exportDocuments(java.io.File, String, java.io.File)
     */
    private File hibernateConfig;

    /**
     * @parameter default-value = "${project.build.directory}/export"
     * @see com.xpn.xwiki.tool.backup.Exporter#exportDocuments(java.io.File, String, java.io.File)
     */
    private File exportDirectory;

Here's the javadoc for the parameters:

     * @param exportDirectory the directory where to export the documents
     * @param databaseName some database name (TODO: find out what this name is really)
     * @param hibernateConfig the Hibernate config fill containing the database definition (JDBC
     *        driver, username and password, etc)

3) Run mvn xwiki-packager:import  and xwiki-packager:export for import and export