Rework template calls for module

[julienbourdeau]

Questions	Answers
Branch?	develop
Description?	$this->smarty in a module class is a very nice feature, you can assign variables and they are not global. Unfortunately $this->display uses hacks to load overrides and cache. This PR introduce $this->fetch which unleash the power of smarty. For a front module the best is described below.
Type?	new feature
Category?	CO
BC breaks?	no
Deprecations?	no
Fixed ticket?
How to test?

If your module is loading front template, do:

$this->fetch('module:modulename/path/to/template.tpl');

It will make theme override much more powerful! (read the doc for further information).

Wrapper.tpl

I also removed the wrapper tpl so modulefrontcontroller can call theme templates like catalog/product.tpl for instance.

[maximebiloe]

Thank you!