Create default topSites for new tab page

[cezaraugusto]

• 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).

Fix #5594

Auditors: @bsclifton

@bradleyrichter:

• I edited topSites icon default size, from 32px to 64px. It affects not only default topSites but any other site. Can be changed as needed;
• Default sites' icon are now stored within Brave. I used arbitrary icons, can also be changed as needed.

Test Plan:

1. On a fresh (clean session-store) view, new tab should have a default grid with 6 sites,
   being them described on referenced issue
2. Visiting a new site should override previous grid
3. If session-store is previously populated, default topSites shouldn't appear on grid

Note: Since we're having some issues with accessed sites, it may be required to refresh the new site in order for (2) to work

[bbondy]

This needs to be rebased please

[bbondy]

@bradleyrichter did we decide on these top sites?
I would put the iOS app instead of youtube

[bbondy]

If we are going with these I think we should cache these tile icons as well so we don't send requests to these places without a user visiting them. @bradleyrichter ?

[bradleyrichter]

@bbondy and we could use larger favicons so the initial view is crispy...

[bradleyrichter]

I think youtube is going to get more traffic than facebook but I will ask Catherine.

[bradleyrichter]

Catherine suggested to swap Git for iOS app store, and this matches BE's opinion.

[bsclifton]

Change looks good- only concern I have (@bbondy, @bradleyrichter) is this. We could show the default sites in two ways:

1. Only show the default sites if you have 0 sites. As soon as you have 1, they all disappear.
2. Show the 6 default sites and then have the user's sites take priority over them. ex: if the user has only 2 top sites showing, grab 4 of the default ones.

This PR is doing option 1... is that what we'd like? I personally would prefer option 2, but I'm curious what you all think 😄

Besides that, all that's left is the feedback from @bbondy; we can likely put a high res copy of the favicon into app/extensions/brave/img/. (I wouldn't say this is blocking- but a user did reach out to support, asking why does Brave make requests for these)

Here's what it looks like right now; notice the default sites have a larger favicon size (64px x 64px):

[bradleyrichter]

please change to #2.

And when we have freceny done, the defaults will stay around longer and not be replaced even before a user sees them for the second time

@garvankeeley may have comments related to his improvements over the same issues with iOS top sites.

[bbondy]

Still needs to load icons not remotely, moving this to 0.12.11

[cezaraugusto]

PR updated.

@bbondy sites' icon are now stored within the app;
@bradleyrichter I updated this PR resume with info about design changes I did. All open for new changes per request.
@bsclifton code ready for review

[bsclifton]

This is never used, can you remove it pls? 😄

[cezaraugusto]

@bsclifton thanks, updated

[bsclifton]

Looks good to me 😄