Create namespaces of grouped metadata for the rose GUI

This might be more intuitive for the user than having everything in "template variables".

Currently there is one called "AutoAssess", but we probably don't need this one, as the title should be more global.

We probably need one for "years".

We should hide testing, and put "max parallel tasks" and "raw data dir mode" in an ESMVAlTool specific section.

Info:
- Example metadata for workflow control:: https://code.metoffice.gov.uk/trac/roses-u/browser/e/a/2/1/0/trunk/meta/rose-meta.conf

You can have metadata to show "namelist" as something else, using `title=`.

**Implementation ideas**
Include the following sections:
- `Required`
- `Datasets`
- `ESMValTool`