Issue: In page Uphold flow vs. using tabs

[mandar-brave]

To reduce in tab errors and managing workflows to send user back, it would be good to have the Uphold flow in-page vs. via creating new tab for every single call (auth, reg, kyc, etc.).

The current UX on this is bad; Prioritizing to land within 0.69 dev timeframe!

@NejcZdovc

[GeetaSarvadnya]

Verification passed on

Brave	0.69.113 Chromium: 76.0.3809.100 (Official Build) beta (64-bit)
Revision	ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990}
OS	Windows 10 OS Version 1803 (Build 17134.523)

• Verified the test plan from Open uphold links in the same tab brave-core#3069

• Verified uphold page displayed in the same tab when verifying wallet by clicking on Verify wallet in the brave://rewards page

• Verified uphold page displayed in the same tab when verifying wallet by clicking on Add funds in the brave://rewards page

• Verified uphold page displayed in the same tab when verifying wallet by clicking on Withdraw Funds in the brave://rewards page
  

• Verified uphold page displayed in the new tab when verifying wallet by clicking on Verify wallet in the BR panel

• Verified uphold page displayed in the new tab when verifying wallet by clicking on Add funds in the BR panel
  

Verified passed with

Brave	0.69.114 Chromium: 76.0.3809.100 (Official Build) beta (64-bit)
Revision	ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990}
OS	Mac OS X

• Verified the test plan from Open uphold links in the same tab brave-core#3069
• Verified when clicking on Verify Wallet or Add Funds from panel (via BAT logo) new tab was opened which sent user to Uphold.
• Verified when clicking on Verify Wallet, Add Funds, Withdraw Funds, or (verify), user was directed to Uphold in the existing (brave://rewards) tab.

Verification passed on

Brave	0.69.114 Chromium: 76.0.3809.100 (Official Build) beta (64-bit)
Revision	ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990}
OS	Ubuntu 18.04 LTS

• Verified the test plan from Open uphold links in the same tab brave-core#3069
• Verified when clicking on Verify Wallet or Add Funds from panel (via BAT logo) new tab was opened which sent user to Uphold.
• Verified when clicking on Verify Wallet, Add Funds, Withdraw Funds, or (verify), user was directed to Uphold in the existing (brave://rewards) tab.