Wallet: Add form for adding assets to balances

[veado]

TODO

• (1) Create AddAssetForm component.
• (2) Persistent state of added token

Screenshot

Note: We won't start with ERC 20 tokens, but with BTC and BNB assets. Ignore ERC 20 tokens in labels and texts at following layouts for now.

Autocomplete

Error

Success

Mobile

^ All layouts at FIGMA: https://www.figma.com/file/LgRqZCGMShZ2mJ702MIqyV/ASGARDEX-2020?node-id=1306%3A7469