TC: limited/configurable list of allowed plugins and filters

A specfic list of deemed safe TT Plugins and Filters are now allowed to
be used within templates. These are also configurable as
RapidApp::Template::Controller config params:

  allowed_plugins => ARRAYREF
  allowed_filters => ARRAYREF

It is very important to not allow plugins like 'Datafile' which allow
reaching into the filesystem, but there are still other plugins which
are safe and are very useful, like Format, HTML, etc, so these can be (and
are by default) enabled on a case-by-case basis