IPVanish support (#475)

- Fix #410 and #416

internal/provider/ipvanish/provider.go

@@ -0,0 +1,19 @@
+package ipvanish
+
+import (
+	"math/rand"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type Ipvanish struct {
+	servers    []models.IpvanishServer
+	randSource rand.Source
+}
+
+func New(servers []models.IpvanishServer, randSource rand.Source) *Ipvanish {
+	return &Ipvanish{
+		servers:    servers,
+		randSource: randSource,
+	}
+}