Add dashiki config generation

Usage:
    scripts/admin dashiki
        -- gets project and metric configuration for WikimetricsBot,
           limited to scheduled reports

    scripts/admin dashiki --all-config
        -- gets all project and metric configuration

Also added a category field to each metric in order to be able to
group them into categories.  Also added a default_submetric field to
metrics that do not have their results in a dictionary keyed on their
id.

Change-Id: Iaf57ff4af1fb9452071236f156dd843c5d1cedff