Allow stake amount equal to min stake

[cygnusv]

Currently, the smart contract only allows to stake amounts strictly greater than the min stake, which is weird from UX perspective.

Related: threshold-network/token-dashboard#103

[cygnusv]

The fix will be included in the next release of the staking contract, but in the meantime we can just set the min stake to 39,999.999999 T as a workaround