Make AnalyticsMeta match RFC

Have several Option fields here that don't need to be.  Analytics service says results will be:

struct AnalyticsQueryResult {

    rows: Iterable[AnalyticsQueryRow],

    errors: Iterable[JsonObject],

    warnings: Iterable[JsonObject],

    signature: Object,

    requestId: String,

    clientContextId: String,

    status: String,

    info: AnalyticsMetrics,

} 

Changes we need to make to match the RFC and what analytics return include:

• Returning individual warnings rather than a blob of JSON.
• Possibly reporting individual errors.  It's currently unclear in the RFC is this is required, but the response here does suggest multiple errors can be returned.
• Making several Option fields non-Optional - metrics (this is different to query, where metrics can be disabled), clientContextId, signature.