Misc permalinks adjustments

* Move config loading to the page package
* Fix a lower bound panic for the `:sections` slice syntax.
* Always return the `:title`
* Add some permalinks integration tests
* Also see issues below

Fixes #9448
Fixes #11184
See #8523

hugolib/content_map.go

@@ -680,7 +680,14 @@ func (m *contentMap) splitKey(k string) []string {
 		return nil
 	}
 
-	return strings.Split(k, "/")[1:]
+	parts := strings.Split(k, "/")[1:]
+	if len(parts) == 0 {
+		return nil
+	}
+	if parts[len(parts)-1] == "" {
+		parts = parts[:len(parts)-1]
+	}
+	return parts
 }
 
 func (m *contentMap) testDump() string {