Follow Freemarker best practices regarding file extensions, output formats, and auto-escaping

Per HSTTWO-3422 we upgraded to Freemarker 2.3.24, one of the reasons being a new feature: auto-escaping.

Further investigation revealed that some more work is needed, see:

http://freemarker.org/docs/dgui_misc_autoescaping.html
http://freemarker.org/docs/pgui_config_outputformatsautoesc.html

FreeMarker automatically escapes all values printed with ${...} if it's properly configured (that's the responsibility of the programmers; see here how). The recommended practice is using ftlh file extension to activate HTML auto-escaping, and ftlx file extension to activate XML auto-escaping.

In an 11.1 archetype project, I had to make the following changes to get this working:

Add *.ftlh to the web files includedFiles configuration.

Add a *.ftlh url-pattern for the freemarker servlet-mapping in the site web.xml:

  <servlet-mapping>
    <servlet-name>freemarker</servlet-name>
    <url-pattern>*.ftl</url-pattern>
    <url-pattern>*.ftlh</url-pattern>
  </servlet-mapping> 

Add to the FreemarkerServlet in site web.xml:

    <init-param>
      <param-name>incompatible_improvements</param-name>
      <param-value>2.3.24</param-value>
    </init-param>

Furthermore, any default Freemarker template would have to be changed to *.ftlh extension, and content output now using ${foo?html} changed to ${foo}. I created ESSENTIALS-1054 for that.