Default pagination for backend and frontend are different.

[serdula]

Describe the bug

Default pagination for backend is 20:

	private static final Integer DEFAULT_PAGE_SIZE = 20;

Default pagination for fronted is 25:

	export const PER_PAGE = 25;

This result in this behavior:

1. When you first open the topics list in the browser you get 20 topics (1…20)
2. When you click the “Next page” you get 25 topics from 25 to 50
3. If you want to see topics 21...25 you need to click “Previous” to see them
4. If you happen to have 21...25 topics the next page is empty

Set up
docker master image

Expected behavior
Default pagination for backend and frontend should be same.