Refactor template helper() function

[Johan Janssens]

The template helper()function uses a none standard identifier syntax, where the function to be called is appended at the end, eg [ext:package.template.helper.name.function]which can be a bit confusing.

Refactor to follow the standard syntax [ext:package.template.helper.name] or shorthand [name.function]for build in helpers. instead of adding the function, return the helper object and allow the function to be called on the helper. Example;

<?= helper('ext:package.template.helper.name.function') ?>

becomes

<?= helper('ext:package.template.helper.name')->function(); ?>