Add LndHub db/models, and quick stats for admin views

app/models/lndhub_user.rb

@@ -0,0 +1,15 @@
+class LndhubUser < LndhubBase
+  self.table_name = "users"
+  self.inheritance_column = :_type_disabled
+
+  has_many :accounts, class_name: "LndhubAccount",
+                      foreign_key: "user_id"
+
+  belongs_to :user, class_name: "User",
+                    primary_key: "ln_account",
+                    foreign_key: "login"
+
+  def balance
+    accounts.current.first.ledgers.sum("account_ledgers.amount")
+  end
+end