[HH-54][PLACES] Save itineraries in DB

[cristighr1995]

In this PR we save in the database the users' returned itineraries. The purpose of doing this is for future data processing, statistics and recommendations.

Right now the CalculatedItineraries table contains the following information:

• id (unique identifier for a plan to avoid duplicates)
• city name
• timestamp (the date of the plan)
• itinerary (json format of ordered list of places with moving & visiting time information)

• stats

  Also, we can find the cacheItineraries API call, in which we prefetch itineraries from the DB.

[cristighr1995]

Related issue: https://github.com/cristighr1995/Holiholic/issues/54