feat(uphold): align Uphold and Coinbase portals

[Syn-McJ]

Issue being fixed or feature implemented

Uphold portal UI needs to be unified with Coinbase and the Topper widget added as the Buy option.

What was done?

• CoinbaseViewController is refactored into IntegrationViewController to be shared across Coinbase and Uphold.
• Integration VC and Buy&Sell portal VC are moved into a separate storyboard.
• Coinbase and Uphold models are refactored to derive from the same parent class.
• Integration Portal UI is aligned with the latest design.
• Obsolete Uphold code is removed.
• Some bugs with displaying Uphold balance on the Buy&Sell screen are fixed.
• OTP input for Uphold is changed to submit automatically after 6 digits are entered.

How Has This Been Tested?

QA

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[pankcuf]

LGTM