Handling Enums for transfer restrictions

[bitbeckers]

Currently we don't expose the Transfer restrictions in the SDK.

• Enums are expected as BigNumber input
• Enums are not exposed via the ABI
• We use enums to define transfer restriction so we should make handling these reasonably foolproof

[Jipperism]

@bitbeckers would you agree this is finished?

[bitbeckers]

@Jipperism is there a definition available in the SDK? For instance a mapping from String to BigNumber?

[Jipperism]

@bitbeckers it lives in the frontend. Probably nice to add it to the SDK so it's clear for others as well.