Fix nomethod related bug

The change introduced in 66e4bac0fd5f8a24b02b4641ee06a74dae63c8b4
that changed the drinks_controller.rb file, in method set_drink
from `@drink = Drink.find(params[:id])` to
`self.resource = Drink.find(params[:id])` caused an nomethod
exception, which basically broke any view related to a single
drink. This reverts that change.

A quick google search tells me that this self.resource way of doing
things is related to devise. (Not sure that is the case though.)
Move menu items, add .present? check to beer of the moment

This prevents the page from crashing when there is no beer
available.