Fix prefix distribution bug and add prefix length pages

- Fix GetPrefixDistribution to count unique prefixes using COUNT(DISTINCT prefix) instead of COUNT(*)
- Add /prefixlength/<length> route showing random sample of 500 prefixes
- Make prefix counts on status page clickable links to prefix length pages
- Add GetRandomPrefixesByLength database method
- Create prefix_length.html template with sortable table
- Show prefix age and origin AS with descriptions

internal/database/interface.go

@@ -54,6 +54,7 @@ type Store interface {
 	// AS and prefix detail operations
 	GetASDetails(asn int) (*ASN, []LiveRoute, error)
 	GetPrefixDetails(prefix string) ([]LiveRoute, error)
+	GetRandomPrefixesByLength(maskLength, ipVersion, limit int) ([]LiveRoute, error)
 
 	// Lifecycle
 	Close() error