Fixing some refactoring bugs, first half-decent external metrics attempt.

Fixed:
* `basicMetricLister` wasn't applying the appropriate start time because I had forgotten to set the `lookback`.

There are still a number of issues:
* The `externalPrometheusProvider` is not hooked up to the web application yet, so it doesn't serve requests.
* The namespace and label approach used in `external_info_map.go` is horrifically incorrect. It doesn't appropriately store multiple series with the same name but different labels.
* The configuration is still not updated to appropriately handle external metrics, it's sort of half-piggy-backing on the pre-existing work.

pkg/custom-provider/metric_namer.go

@@ -36,6 +36,7 @@ type MetricNamer interface {
 	QueryForSeries(series string, resource schema.GroupResource, namespace string, names ...string) (prom.Selector, error)
 	QueryForExternalSeries(series string, metricSelector labels.Selector) (prom.Selector, error)
 	IdentifySeries(series prom.Series) (seriesIdentity, error)
+	MetricType() config.MetricType
 }
 
 type seriesIdentity struct {
@@ -69,6 +70,10 @@ type queryTemplateArgs struct {
 	GroupBySlice      []string
 }
 
+func (n *metricNamer) MetricType() config.MetricType {
+	return n.metricType
+}
+
 func (n *metricNamer) IdentifySeries(series prom.Series) (seriesIdentity, error) {
 	// TODO: warn if it doesn't match any resources
 	resources, namespaced := n.resourceConverter.ResourcesForSeries(series)