Fix sort order width

[CasperWA]

The sort order button is a fixed width, which will clash if the CSS is changed.
This has already been observed using the materialscloud template.

This PR also adds a --template option to the optimade-client CLI, where one can pass a Voilà template.

[codecov]

Codecov Report

Merging #226 (ba46990) into develop (a7a3e2e) will increase coverage by 0.06%.
The diff coverage is 75.00%.

@@             Coverage Diff             @@
##           develop     #226      +/-   ##
===========================================
+ Coverage    35.82%   35.89%   +0.06%     
===========================================
  Files           18       18              
  Lines         2272     2276       +4     
===========================================
+ Hits           814      817       +3     
- Misses        1458     1459       +1     

Flag	Coverage Δ
optimade-client	35.89% <75.00%> (+0.06%)	⬆️

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Impacted Files	Coverage Δ
optimade_client/subwidgets/sort_selector.py	34.09% <ø> (ø)
optimade_client/cli/run.py	95.65% <75.00%> (-1.97%)	⬇️

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