Add support and migration for lndhub.go

Slightly WIP

app/services/lndhub.rb

@@ -2,7 +2,7 @@ class Lndhub
   attr_accessor :auth_token
 
   def initialize
-    @base_url = ENV["LNDHUB_API_URL"]
+    @base_url = ENV["LNDHUB_LEGACY_API_URL"]
   end
 
   def post(endpoint, payload)
@@ -42,15 +42,15 @@ class Lndhub
     self.auth_token
   end
 
-  def balance(user_token)
+  def balance(user_token=nil)
     get "balance", user_token || auth_token
   end
 
-  def gettxs(user_token)
+  def gettxs(user_token=nil)
     get "gettxs", user_token || auth_token
   end
 
-  def getuserinvoices(user_token)
+  def getuserinvoices(user_token=nil)
     get "getuserinvoices", user_token || auth_token
   end