Allowances - Revoke - UI

[ezra-sg]

blocked by #206

Create a modal UI for editing the allowances for an asset

• there should be a pencil icon next to the amounts in the table, which has proper a11y
• clicking the pencil icon in the table should launch a modal for that asset
  • modal should be its own component, something like EditAllowanceModal
• the modal title should be "Define new {symbol | asset name up to 20 characters} allowance for {spender contract - external link}"
• there should be three options, None Unlimited and Custom (all should be added to i18n)
• custom should have a currency input which is disabled unless Custom is selected
  • if you edit the token amount input, then click a different option like None, the token amount input should be cleared
• TODO should there be any constraints on the currency input, like number of decimals? limit to 999T, max decimals is decimals for contract. for NFTs, only integers allowed
• confirm should do nothing (implemented in Allowances - Revoke - API Integration #606)
• cancel and clicking outside the modal should close the modal

Update allowances table to include revoke checkboxes

• allowances table should get a new column for selecting rows
• clicking the checkbox in the header cell should select all visible rows
• the table controls at the foot of the table should be updated to include a new layout to allow for arbitrary text, like 'x rows selected' (see below image)