Pool navigation & listing improvements

[po5]

Building upon #537 with some aspects from #403.
Has been in use for about two years on a mid-sized public instance.

Notable changes new to this PR:

• Polished stacked thumbnail display for pool list, with hover/focus animation
• Allows negating sort:pool
• Uses the correct pool when overriding navigation
• Fixed issue where nearby pool posts would take a very long time to resolve
• No longer makes an extra request to get surrounding pool posts

TODO list:

• Custom thumbnail functionality for pools (allow setting a post ID to be used as a singular thumbnail)
• UI for adding, removing, and rearranging posts from a pool
• Search by pool name instead of ID
• Fancy display name for pools (may be specific to my use case, but I want separate display names from search tokens)
• Investigate if the query can be made more efficient

Notes:
Post navigation override seems redundant, we can just have sort:pool in the pool navigator's search links? Should lead to the same sorting.

[G1org1owo]

Tried this in the hope it'd also fix the pool page loading pretty damn slow (and I still have no clue why) and got this when trying to change the pool category of an empty pool:

Which causes the "Save changes" button to hang until the page is reloaded.

[po5]

Good catch. I'll account for this in a later commit, for now reverting ff788a5 should fix it. But that is the commit that improves pool listing loading performance, lol.

[G1org1owo]

Damn, what a world we live in lol

Another one I found when trying to update the content of a post:

By having a quick look at occurences for hasPostId in the repo it doesn't seem like anything has changed, no clue about this
Nevermind, I just realized that the error above most likely doesn't mean that posts doesn't have a function hasPostId anymore for some reason, but that posts is now a different kind of object (microposts?), which would mean the above commit is likely the cause for this aswell.

[G1org1owo]

Can confirm reverting ff788a5 fixes both issues.

[enzof2003]

I know I'm technically necroposting, but the issue of Uncaught TypeError: t.detail.pool.posts.clear is not a function can be fixed with a rather simple band-aid solution without reverting #ff788a5

In client/js/models/pool.js
get posts() { return this._postsMicro || this._posts; }
Can be replaced by
get posts() { return this._posts; }

Which allow the code to find the correct functions, this is purely a quick fix that I haven't had time to thoroughly test so please be incredibly careful if setting this up on a large production instance