Fixing 'enumerate' environment

The class enables to select between the standard LaTeX 'enumerate'
environment and the override provided by upmethodolody: the
class option 'standardlists'.
The override of the 'enumerate' environment was created with the
tools provided by the package 'environ' (issue #18). The overriding is
delayed to the begining of the document.
Fixing the 'description' environment.

The override of the 'description' environment is created with the tools
provided by the 'environ' package. This overriding is delayed to the
begining of the document. This commit fixes the issue #19.