Initial hot reloading / preview for webui within brave-core

[petemill]

Overall tracked with #2335

Create a storybook in brave-core to contain src/features from brave-ui

This is not an issue to request hot-reloading in the browser webui's itself, that will require a bit of change to get files served from localhost instead of internal build-produced pak files!

[LaurenWags]

@petemill is manual QA needed for this one? Looks like maybe the first test plan in brave/brave-core#2857 can be executed on a packaged build, but not the others. is that sufficient?

[petemill]

@LaurenWags yes just checking NTP works should be enough, thanks

[LaurenWags]

Verified passed with

Brave	0.69.119 Chromium: 76.0.3809.132 (Official Build) beta (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Mac OS X

• Verified first test plan listed in New Tab Page: Move from brave-ui to brave-core brave-core#2857

Verification passed on

Brave	0.69.121 Chromium: 76.0.3809.132 (Official Build) beta (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Ubuntu 18.04 LTS

• Verified first test plan listed in New Tab Page: Move from brave-ui to brave-core brave-core#2857

Verification passed on

Brave	0.69.121 Chromium: 76.0.3809.132 (Official Build) beta (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Windows 10 OS Version 1803 (Build 17134.523)

• Verified first test plan listed in New Tab Page: Move from brave-ui to brave-core brave-core#2857