Get details for a Spot from an id

[Lillith13]

Returns the details of a spot specified by its id.

• [x] Successful response includes data only for the specified spot
• [x] Spot data returned includes the id, ownerId, address, city, state, country, lat, lng, name, description, price, createdAt, and updatedAt
• [x] Spot data returns aggregate data for numReviews and avgStarRating
• [x] Spot data returns associated data for SpotImages, an array of image data including the id, url, and preview
• [x] Spot data returns associated data for Owner, including the id, firstName, and lastName
• [x] Error response with status 404 is given when a spot does not exist with the provided id

[Lillith13]

• [x] finish adding appropriate associations