Port Backend to SQLite/Sequelize (removes MongoDB), Support Electron (#14)

* The MongoDB/Mongoose data storage is removed in favor of Sequelize. This abstracts over SQLite or RDBMs like PostgreSQL and MSSQL. The default is SQLite, which significantly simplifies deployments in end-user environments.

* As Spacedeck now has no more mandatory server dependencies, we can wrap it in Electron and ship it as a desktop application.

* Removes docker-compose.yml

* First version of import UI

models/action.js

@@ -1,5 +1,7 @@
 'use strict';
 
+// FIXME port this last model
+
 var mongoose = require('mongoose');
 var Schema = mongoose.Schema;