Work on #12: Move each providers in their own packages

alerting/provider/twilio/twilio_test.go

@@ -0,0 +1,19 @@
+package twilio
+
+import "testing"
+
+func TestTwilioAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{
+		SID:   "1",
+		Token: "1",
+		From:  "1",
+		To:    "1",
+	}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}