Add support for grouped recipes #277
Description
In ESMValTool, recipes can either be stored in the top level recipe directory (e.g. esmvaltool/recipes/recipe_name.yml), or they can be grouped in subdirectories (e.g. esmvaltool/recipes/recipe_group/recipe_name.yml) making run commands esmvaltool run recipe_name.yml and esmvaltool run recipe_group/recipe_name.yml respectively.
CMEW constructs the recipe name by prepending recipe_ and appending .yml to the assessment area variable defined in the flow.cylc. If the assessment area is 'name' then CMEW can construct recipe_name.yml, but it currently has no concept of groups. / also can't be used in a task parameter value.
This is of relevance to the porting of the Climate Model Monitor because the ESMValTool monitor recipe is itself a grouped recipe.
See RTW for solution (ask Alistair for more info)