Reduce fetchLimit (40 -> 20)

[sunaurus]

This PR proposes reducing the default page size. It's certainly a change with some trade-offs, so feel free to reject it (or debate the extent of the reduction), but I will provide my argument below:

On lemm.ee, I have noticed that this small tweak has vastly improved the experience for our users. By reducing the page size in half, our page loads significantly faster, and server load has in general decreased slightly as well.

I will also share some actual stats. This was with fetchLimit set to 40:

And this is the same test run with fetchLimit reduced to 20:

Of course, the downside with this is that users need to load additional pages more often, but it seems like a small price to pay considering the performance benefits.

[dessalines]

I'm good with this. I know the solution to optimize our post_view queries now, but that might be a week or two yet till I can add it.

[SleeplessOne1917]

This seems like a good short term solution. I think part of the problem is also that postviews are very big blobs of json, so even fetching a few is going to mean a big response from the API.