DRY up btcpay and lndhub services

Removing initialize methods from the main/manager class also allows for
different iniitalizers in specific task services

app/services/lndhub.rb

@@ -1,24 +1,20 @@
-class Lndhub
+class Lndhub < ApplicationService
   attr_accessor :auth_token
 
-  def initialize
-    @base_url = ENV["LNDHUB_API_URL"]
-  end
-
-  def post(endpoint, payload)
+  def post(path, payload)
     headers = { "Content-Type" => "application/json" }
     if auth_token
       headers.merge!({ "Authorization" => "Bearer #{auth_token}" })
     end
 
-    res = Faraday.post "#{@base_url}/#{endpoint}", payload.to_json, headers
+    res = Faraday.post endpoint_url(path), payload.to_json, headers
     log_error(res) if res.status != 200
 
     JSON.parse(res.body)
   end
 
-  def get(endpoint, auth_token)
-    res = Faraday.get("#{@base_url}/#{endpoint}", {}, {
+  def get(path, auth_token)
+    res = Faraday.get(endpoint_url(path), {}, {
       "Content-Type" => "application/json",
       "Accept" => "application/json",
       "Authorization" => "Bearer #{auth_token}"
@@ -42,7 +38,7 @@ class Lndhub
     self.auth_token
   end
 
-  def balance(user_token=nil)
+  def fetch_balance(user_token=nil)
     get "balance", user_token || auth_token
   end
 
@@ -72,4 +68,14 @@ class Lndhub
       Sentry.capture_message("Lndhub API request failed: #{res.body}")
     end
   end
+
+  private
+
+    def base_url
+      @base_url ||= Setting.lndhub_api_url
+    end
+
+    def endpoint_url(path)
+      "#{base_url}/#{path.gsub(/^\//, '')}"
+    end
 end