[TASK-788] Fix Library pagination

Checklist

[ ] If you've added code that should be tested, add tests
[ ] If you've changed APIs, update (or create!) the documentation
[x] Ensure the tests pass
[x] Make sure that your code lints and that you've followed our coding style
[x] Write a title and, if necessary, a description of your work suitable for publishing in our release notes
[ ] Mention any related issues in this repository (as #ISSUE) and in other repositories (as kobotoolbox/other#ISSUE)
[ ] Open an issue in the docs if there are UI/UX changes

Fixed pagination not appearing for My Library, Public Collections and Single Collection, thus blocking users from accessing items after page 1.

There is a small fix in one commit, and UI improvement in other (replaced buttons with new Button component in the AssetsTable footer)

Testing:

A lot of (more than 100) library items:
- Please use many small.zip
- Drop whole 40 files onto My Library and let it upload (might take a while, might freeze your local environment)
- Repeat two more times, or until you have enought to see and use pagination
Huge (more than 100 items) collection:
- Drop HUGE_COLLECTION.xlsx file onto My Library
- It would ask you to choose type, just click ok (this is a bug - not recognizing this XLSX file is a collection - that I will fix in other PR)
- Let it process it; it will take some time, and probably you would need to reload browser tab to see it - the collection has almost 2000 items :)
- Navigate inside the collection and test the pagination (should be in the footer of the table of assets)
A lot of public collections:
- This one is harder to test, as there is no easy way to have 100+ public collections
- Just create 4-5 collections, enter each and use "Make public" button (there is a bug with it - see #4964)
- In the code in publicCollectionsStore.ts temporarily change PAGE_SIZE = 100 to PAGE_SIZE = 2 to see pagination in action
- This method actually works for two other points too 🙃