Improve distance leaderboard algorithm

[diogogmatos]

Currently, the distance leaderboard calculates the score of a user by doing the sum of distances from the CeSIUM "headquarters" to their pins.

This means that the more pins someone places close together to each other, the higher their score will be, which is unfair since we want to value distance traveled to place a pin and not quantity of pins.

Some better alternatives would be:

• Group pins from the same person that are placed close together, calculating the average distance of the pins to the headquarters.
• Same as the previous solution, but instead choose the highest distance from the group of pins.
• Same as the previous solution, but instead choose the lowest distance from the group of pins.

To group the pins, there could be two alternatives:

• Create the concept of "trip" and make users manually mark a group of pins as belonging to the same trip on the submission process. Pins from the same trip would be grouped and count as a single distance.
• Mathematically try to group pins from the same user by checking, for each pin, if there are others close by (the radius could be specified to a specific distance).