Define the correct amount of days for subscription period

[StErMi]

@dannypostma you have defined the subscription period as 1 month. In solidity, we have translated to 31 days that could be incorrect because if you subscribe for 12 months it would be 372 days.

@dannypostma if we change the period (1 month) to 365.25 days / 12 should we also change the value of STAKE_LOCK_PERIOD in RareBlocksStaking to that value?