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

routes/api/memberships.js

@@ -1,56 +1,40 @@
 "use strict";
 
 var config = require('config');
-require('../../models/schema');
 
-var fs = require('fs');
-var _ = require("underscore");
-var mongoose = require("mongoose");
 var async = require('async');
-var archiver = require('archiver');
-var request = require('request');
 var url = require("url");
 var path = require("path");
 var crypto = require('crypto');
-var qr = require('qr-image');
 var glob = require('glob');
-var gm = require('gm');
 
 var express = require('express');
 var router = express.Router();
 
-var userMapping = { '_id': 1, 'nickname': 1, 'email': 1};
-var spaceMapping = { '_id': 1, name: 1};
+const db = require('../../models/db');
+const Sequelize = require('sequelize');
+const Op = Sequelize.Op;
+const uuidv4 = require('uuid/v4');
 
 router.get('/:membership_id/accept', function(req, res, next) {
   if (req.user) {
-    Membership.findOne({
+    db.Membership.findOne({where:{
       _id: req.params.membership_id,
-      state: "pending",
-      code: req.query.code,
-      user: { "$exists": false }
-    }).populate('space').exec((err,mem) => {
-      if (err) res.sendStatus(400);
-      else {
-        if (mem) {
-          if(!mem.user) {          
-            mem.code = null;
-            mem.state = "active";
-            mem.user = req.user;
-            
-            mem.save(function(err){
-              if (err) res.status(400).json(err);
-              else {
-                console.log(mem);
-                res.status(200).json(mem);
-              }
-            });
-          } else {
-            res.status(400).json({"error": "already_used"});
-          }
+      code: req.query.code
+    }, include: ['space']}).then((mem) => {
+      if (mem) {
+        if (!mem.user) {
+          mem.state = "active";
+          mem.user_id = req.user._id;
+          
+          mem.save().then(function() {
+            res.status(200).json(mem);
+          });
         } else {
-          res.status(404).json({"error": "not found"});
+          res.status(200).json(mem);
         }
+      } else {
+        res.status(404).json({"error": "not found"});
       }
     });
   } else {