Add Gitea integration

Support for Gitea organization hooks, based on GitHub hooks code.

closes #24

index.js

@@ -149,6 +149,7 @@ module.exports = async function(robot) {
   //
 
   require('./integrations/github')(robot, kredits);
+  require('./integrations/gitea')(robot, kredits);
 
   if (typeof process.env.KREDITS_MEDIAWIKI_URL !== 'undefined') {
     require('./integrations/mediawiki')(robot, kredits);