Stake: Consolidate stakes from the same day

[gangov]

sometime users stake multiple times in a short period of time, we should calculate the median of such stakes and consolidate them, similar to what we did for the stakes older than 60 days (#403)

[ethsdev]

Hi, @gangov, sorry for leaving comment here without your agreement and respecting the team rule. Because I wanna join your team as full time dev, so I am going to solve issues and challenges as proving of my skill. Could you give me some issue to be solved quickly as test task?