Redesign thread paginator

[rafalp]

Fixes #1586

Adds new paginator to thread page, that makes users aware of page they are on:

Also changes thread template so paginator is also displayed on the top, but its only visible when thread has other pages.

Todo:

• Fix long central button text overflowing whole paginator
• Add secondary toolbar under first one on thread page with option to go back to top (and maybe go back to category)

[coveralls]

Coverage: 98.441% (+0.0002%) from 98.441% when pulling 7ef2127 on fix-1586-new-thread-paginator into c402855 on main.