Reorganize and add migration

Former-commit-id: 807d525f11b5306c2a4a2e7097a8d92d026fc9df [formerly 9c40fcf478e90dd062c9a173b4d563a4ba15b8bc] [formerly 0c56b23e0782fe14717c243d149983185fe9ad2d [formerly 7f4acdda9a]]
Former-commit-id: 71ae3d9712ec1b7203e6483ad586aeef319fba08 [formerly e633558e9a7491044e324ceeb2cb699b2130f1c8]
Former-commit-id: 8e483f94bf5c75d62d00219085d1e68c4e5683c7

utils.go

@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"net"
+	"os"
 	"strings"
 	"time"
 
@@ -201,3 +202,15 @@ func DecryptString(toDecrypt string, password string) (string, error) {
 	bDecrypted, err := cryptopasta.Decrypt(contentData, &key)
 	return string(bDecrypted), err
 }
+
+// exists returns whether the given file or directory exists or not
+func exists(path string) bool {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true
+	}
+	if os.IsNotExist(err) {
+		return false
+	}
+	return true
+}