Contact deletion function.

The following 4 diffs will be landed in quick succession.

• D11266 Contact list MVP
• D11323 Rename contacts
• D11324 Delete contacts
• D11321 Export contacts

• open a wallet with an empty contact list and ensure the Export contacts button is not rendered
• add a new contact, verify the Export contacts button is displayed and ensure clicking on this button results in a csv file being generated for download
• add two more contacts and ensure the exported csv file shows each contact delimitered by a comma
• test across browsers and extension/iOS/Android