Make welcome screen show up on first time run

[cezaraugusto]

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.

Auditors: @bsclifton
Close #9423

Test Plan:

npm run test -- --grep="aboutWelcomeReducer"
npm run unittest -- --grep="tabs API unit tests create"
npm run unittest -- --grep="sessionStore unit tests defaultAppState"

Manual test plan:

1. Have your session as-is
2. Open Brave with this PR
3. Open a new tab
4. About welcome shouldn't show
5. Clear session
6. Open Brave
7. New tab should show, followed by about:welcome as the second tab, active
8. Open another tab by any means
9. about:newtab should show alone

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[bsclifton]

Moving to 0.18.x

[luixxiul]

the manual test plan works.

[bsclifton]

@cezaraugusto could you rebase please? I'll def review / merge after that 😄 thanks!

[cezaraugusto]

ok rebased

[bsclifton]

I know this is outside the scope of the pull request, but I wanted to show this:

We'll want to update the website (which is shown in about:welcome) to fix the logo being cropped:

[bsclifton]

Changes look great! 😄

I updated the tests- If everything looks good, please go ahead and merge. Thanks! 😄 👍

[bsclifton]

It might be cleaner to set this above, when the value is gotten from appState. Something like:

const shouldShowWelcomeScreen = process.env.NODE_ENV !== 'test' &&
                                appState.getIn(['about', 'welcome', 'showOnLoad'])

[bsclifton]

actually... nevermind, I have a solution for this 😄

[cezaraugusto]

@bsclifton awesome thanks for updating, looks great