Add padding to all of the contract handles

[FloppyDisck]

Is your feature request related to a problem? Please describe.
While handle functions are encrypted and protect what the users are sending, some values can still be predicted or assumed

Describe the solution you'd like
To preserve user privacy, all of the handle functions should include an optional padding value to make these TXs harder to predict. A good example is the Snip20 spec.

[LasTshaMAN]

Looks like its better to implement this feature once for all contracts (once all/most of them are in place) ? To lower the chance of missing anything.

[FloppyDisck]

Correct, im leaving the issue here for when cleaning up contracts (and closing the remaining issues)

[LasTshaMAN]

I'm not that familiar with how Secret Network smart contracts work, but I thought it might be prudent to mention some existing Shade code doesn't use padding when calling other contracts, for example (second parameter is "optional padding" and is None):

    // if burnable then burn if not ignore
    if burning_asset.burnable {
        messages.push(burn_msg(amount, None, 256,
                               burning_asset.contract.code_hash,
                               burning_asset.contract.address)?);
    }

Can such sub-calls info be somehow linked to the original method I'm executing on Shade smart contract (with Shade code being open-source) ?

[FloppyDisck]

Yup, this also goes under this issue. Basically add padding in our handle functions + snip20 functions that use then