User session service: Add shopping cart and sticker browsing history

[nicolehaugen]

Create a node.js microservice that persist shopping cart data and the "browse" sticker session data - this could be stored in either MySQL (assuming that there is a relationship here) or Redis.

For example, with Redis:

• We can use a Hash based on the user's id as a key; each sticker item\quantity would then be stored for the user.
• For sticker that the user has chosen to add their shopping cart (e.g. their sticker history) - this list of stickers is shown in the Browse tab. The Redis cache can be used for storing a serialized blob of stickers.

Estimate: 3 days