Fix UX issues on models page

[klakhov]

Motivation and context

• Fixed centering of empty block
• Fixed inconsistency in top bar
• Fixed padding of page numbers

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• [] I have updated the documentation accordingly
• [ ] I have added tests to cover my changes
• [ ] I have linked related issues (see GitHub docs)
• [ ] I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[codecov]

Codecov Report

Merging #7164 (81a1569) into develop (a9a98b3) will increase coverage by 0.02%.
Report is 1 commits behind head on develop.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7164      +/-   ##
===========================================
+ Coverage    81.40%   81.43%   +0.02%     
===========================================
  Files          364      364              
  Lines        39904    39910       +6     
  Branches      3699     3702       +3     
===========================================
+ Hits         32485    32500      +15     
+ Misses        7419     7410       -9     

Components	Coverage Δ
cvat-ui	75.54% <ø> (+0.05%)	⬆️
cvat-server	86.95% <ø> (ø)