Confirmations implementation

[tmancey]

Implement Confirmations into Brave Core

[bsclifton]

@tmancey can you add a test plan in here? (or in the PR- and then link to it from the top post)

[tmancey]

Test Plan: https://docs.google.com/document/d/1ym8tTKdwSkKUPEI4O_iD2qLaYFMdsCjsUdEod5ouZIg/edit#

[LaurenWags]

Verified passed with

Brave	0.63.45 Chromium: 74.0.3729.75 (Official Build) beta(64-bit)
Revision	fdb7915642fef8cf997beac2554709d148e3c187-refs/branch-heads/3729@{#754}
OS	Mac OS X

• Verified test plan from Confirmations implementation #3117 (comment)

Verification passed on

Brave	0.63.46 Chromium: 74.0.3729.91 (Official Build) (64-bit)
Revision	03844ed83e02b8add3f4b9cb859a7108d55b2e4d-refs/branch-heads/3729@{#860}
OS	Windows 10 OS Build 17134.523

• Verified test plan from Confirmations implementation #3117 (comment)

Verification passed on

Brave	0.63.46 Chromium: 74.0.3729.91 (Official Build) (64-bit)
Revision	03844ed83e02b8add3f4b9cb859a7108d55b2e4d-refs/branch-heads/3729@{#860}
OS	Linux

• Verified test plan from Confirmations implementation #3117 (comment)