Reader: tweak to combined card

[samouri]

This PR aims to experiment with CombinedCards. One of the goals of combined cards is to make it so that a noisy site cannot overwhelm your following stream. This PR takes that goal and runs with it wayy further

This PR changes the current behavior of CCs in two ways:

• lifts the requirement that combined posts must be consecutive. Instead each site has a maximum number of CARDS_PER_DAY (combined cards counts as 1). As of now its set to 4. Real Example: Lets say you follow uproxx which posts a ton of times per day. Now it will at-maximum be allowed to have 4 separate combined cards throughout the day
• combined cards will group together as many posts that occurred during the allotted timeframe (6 hours currently because 4 cards per day and 24/4 = 6). It will max out at displaying 5.

known brokeness:

• keyboard shortcuts. they currently rely on the original postKey ordering whereas the entire point of this PR is to see how it feels if we break with reverse chronological

After making this PR it made me think of the following stream a bit differently. Instead of being a "complete collection of everything I follow in reverse-chronological order", it become more like a jumping off point to explore the things that I follow.

cc @fraying

edit: the code is currently super messy, so feel free not to look at it 😟

[matticbot]

Test live: https://calypso.live/?branch=try/reader/cc-eclecticity++

[samouri]

Closing branch because of special character ruining calypso.live