LPS-51886 Render templates through a taglib to support ADT in OSGi portlets

Hey @brianchandotcom,

This change suggested by @rotty3000 allows to render Freemarker ADTs that contain JSP taglibs in OSGi portlets. @ealonso has tested it with the RSS portlet, which he's extracting as an OSGi module and it works.

Thx

@juliocamarero @migue