NFT asset fields

**Is your feature request related to a problem? Please describe.**
You can't create an NFT using the reference bitshares web wallet.

**Describe the solution you'd like**
Asset options include the additional fields required by the [Bitshares NFT spec](https://github.com/Bit20-Creative-Group/BitShares-NFT-Specification)

**Describe alternatives you've considered**
Use 3rd party tools

**Additional context**
N/A

Start by reading the BitShares NFT Specification linked in the issue, then locate the reference wallet's asset-options form and compare its fields with the specification. Done means the wallet exposes all additional NFT asset fields required by the specification and can create an NFT without relying on a third-party tool.

Written by the indexing model from the issue text.