The `TransactionViewBalance` component has been split into three
separate components. This was done primarily to make the asset page
easier to implement. Also the name `TransactionViewBalance` didn't
describe this component very well anymore.
Instead of the Ethereum and token-specific logic being in the same
component, the two cases were split into the `EthOverview` and
`TokenOverview` components respectively. They both use the
`WalletOverview` component, which has the structure shared by both
cases.