Performer urls (#4958)

* Populate URLs from legacy fields
* Return nil properly in xpath/json scrapers
* Improve migration logging

pkg/performer/url.go

@@ -0,0 +1,18 @@
+package performer
+
+import (
+	"regexp"
+)
+
+var (
+	twitterURLRE   = regexp.MustCompile(`^https?:\/\/(?:www\.)?twitter\.com\/`)
+	instagramURLRE = regexp.MustCompile(`^https?:\/\/(?:www\.)?instagram\.com\/`)
+)
+
+func IsTwitterURL(url string) bool {
+	return twitterURLRE.MatchString(url)
+}
+
+func IsInstagramURL(url string) bool {
+	return instagramURLRE.MatchString(url)
+}