Add support for claiming a grants

[kylehickinson]

When a grant is available the user can claim it on the settings screen (or a notifications).

This needs to be integrated from both points (solveGrantCaptcha)

No expiration date when claiming ads earnings in the grant claim screen

Blocked by brave/brave-core#3294

[tmancey]

@kylehickinson can you please raise a ticket in brave-browser so we can get this ticket unblocked

[tmancey]

@kylehickinson are we still blocked (see previous comment)

[kylehickinson]

@tmancey Technically, if we want to have a real grant flow implemented, we still need the dev environment (brave/brave-core#3294) which isn't done and so blocked

If we don't care about this and are just going to wait until virtualized grants, then this maybe can be closed in favour of #1654

[srirambv]

• Verification passed on iPhone XR with iOS 13.2 running 1.13(19.11.4.20)
• Verification passed on iPhone 7+ with iOS 13.2 running 1.13(19.11.4.20)
• Verification passed on iPhone 6 with iOS 12.4 running 1.13(19.11.4.20)
• Verification passed on iPad Pro with iOS 13.2 running 1.13(19.11.4.20)
• Verification passed on iPad Pro with iOS 12.4 running 1.13(19.11.4.20)