Remove dependency of go-bindata (#818)

* Use new embed functionality for serving UI assets

* Use new embed functionality for serving resources. Remove dependency on go-bindata

* Remove Go 1.15

resources/embed.go

@@ -0,0 +1,22 @@
+package resources
+
+import (
+	"embed"
+	"io/fs"
+	"io/ioutil"
+)
+
+//go:embed *
+var filesystem embed.FS
+
+func Asset(path string) ([]byte, error) {
+	f, err := filesystem.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	return ioutil.ReadAll(f)
+}
+
+func Assets() fs.FS {
+	return filesystem
+}

resources/external.go

@@ -1,28 +0,0 @@
-// +build !embed
-
-package resources
-
-import (
-	"io/ioutil"
-	"net/http"
-	"sync"
-
-	"github.com/navidrome/navidrome/log"
-)
-
-var once sync.Once
-
-func Asset(filePath string) ([]byte, error) {
-	f, err := AssetFile().Open(filePath)
-	if err != nil {
-		return nil, err
-	}
-	return ioutil.ReadAll(f)
-}
-
-func AssetFile() http.FileSystem {
-	once.Do(func() {
-		log.Warn("Using external resources from 'resources' folder")
-	})
-	return http.Dir("resources")
-}