Implement page summaries (#747)

[victorporof]

Fixes #747

Looking to start landing this incrementally. Here's a first couple of commits.
A few more coming soon after I finish cleaning up.
@bgrins

[bgrins]

Pulled this down. A UI note I noticed first is the extra spacing and separators between the active tab and inactive:

[bgrins]

Is this ultimately planning to land in a branch for a particular experiment or on master?

[bgrins]

Is this ultimately planning to land in a branch for a particular experiment or on master?

Discussed this in the meeting today, and sounds like it's fine to land this on master with the knowledge that we might want to ultimately hide the 'overview' button or other UI elements while testing other features. IOW we can consider the top bar / nav bar changes present here the new 'default' UI. @phlsa please correct me if that's wrong.

[victorporof]

Landed some of the changes in 9770df4

Further commits will follow in this PR.

[victorporof]

Rebased.

[bgrins]

We've decided in the past to not use TOGGLE_* as an action, instead preferring SET_* so that the action log / frontend is more explicit about what it's requesting. See something like SET_URL_INPUT_VISIBLE as an example

[jsantell]

Agreed on this

[bgrins]

Should there be a separator here?

[bgrins]

extra separator when the last tab is selected tab:

[jsantell]

This looks overall good to me -- some visual bugs that Brian pointed out, but easier to fix it with it landed, and can begin tackling the harder issue of custom cards

[jsantell]

@bgrins passed this over to me -- after looking through the code, I don't have really any comments other than the naming of the action and maybe the granularity of some of the views, like Thumbnail and FittedImage, especially as we don't have other consumers of those (yet -- maybe you're anticipating some things). Or maybe just a preference. Either way, some of the lower level components could benefit from brief comment descriptions on how/when to use them (if I'm building something else looking at components, I should be able to quickly know when I'd use thumbnail vs fitted image).

Looks great! Once landed we can file follow up bugs and tackle the custom cards.

[victorporof]

@bgrins
Mockups seem to disagree with you: https://cloud.githubusercontent.com/assets/514315/16498113/82b31796-3efa-11e6-8bba-f112192c28b2.png

But since I'm not really sure, I'll land as is and we can get @phlsa's feedback later.

[victorporof]

@jsantell FittedImage and Thumbnail both have comments that describe what they're intended for.

Granular components are always a good idea, and incredibly useful once we properly start using shouldComponentUpdate. I'd suggest moving forward as we decided in Vancouver: very granular components for everything: better separation of concerns, better performance, better composability, cleaner code.

[phlsa]

I'm not entirely sure what you are referring to @victorporof.
If it's about the separators, the idea is that they disappear when they would be next to a selected tab, much like they do in Firefox today.