Improve SMTP

API can now be started without properly configured SMTP (it complains when it is used)
Send() function can now use alternative dialers (mostly used for testing)
Added mailhog service (make mailhog.up) to ease mail testing
Add default .env example that points to localhost:1025 (mailhog) setup
Proper unit testing

cmd/crm/main.go

@@ -5,13 +5,14 @@ import (
 	"os"
 
 	service "github.com/crusttech/crust/crm"
+	"github.com/crusttech/crust/internal/mail"
 
 	"github.com/crusttech/crust/internal/auth"
 	"github.com/crusttech/crust/internal/rbac"
 )
 
 func main() {
-	flags("crm", service.Flags, auth.Flags, rbac.Flags)
+	flags("crm", service.Flags, auth.Flags, rbac.Flags, mail.Flags)
 
 	// log to stdout not stderr
 	log.SetOutput(os.Stdout)