Consider adding a cap on the size of state variables

[jlevison]

We experienced very bad memory behavior when a single state variable is very big (e.g. 50MB)
depending on the contract, today it is rather simple to DOS the vchain or even in a non-malicious way write contracts which will make the virtual chain unstable.

we should consider to limit state variables to several MB (<10)

[moved from https://github.com/orbs-network/orbs-network-go/issues/1524]