feat(skydiver-profile): add SkydiverProfile MySQL model and service

Introduces the skydiver_profile table as an optional 1-to-1 extension
of the user table, holding skydive-specific fields (licence, poids,
bg_image). Wired up with Sequelize associations and a service with
upsert support. Migration, model, relationships, and service layer
all included.

src/services/index.js

@@ -4,6 +4,7 @@
 exports.ArticleService = require('./mysql/article.service');
 exports.CommentService = require('./mysql/comment.service');
 exports.ProductService = require('./mysql/product.service');
+exports.SkydiverProfileService = require('./mysql/skydiver-profile.service');
 exports.TagService = require('./mysql/tag.service');
 exports.UserService = require('./mysql/user.service');
 //exports.HeroWarService = require('./mysql/herowars.service');