UI: Standarize colors and themify the app(First step)

[timotheeguerin]

[codecov]

Codecov Report

Merging #1485 into master will increase coverage by 0.04%.
The diff coverage is 54.54%.

@@            Coverage Diff            @@
##           master   #1485      +/-   ##
=========================================
+ Coverage   59.06%   59.1%   +0.04%     
=========================================
  Files        1053    1053              
  Lines       24708   24738      +30     
  Branches     3414    3418       +4     
=========================================
+ Hits        14593   14621      +28     
- Misses      10115   10117       +2

Impacted Files	Coverage Δ
app/services/themes/theme.model.ts	75.25% <100%> (+1.34%)	⬆️
...debar/sidebar-content/sidebar-content.component.ts	97.43% <100%> (ø)
...c/@batch-flask/ui/sidebar/sidebar-content/index.ts	100% <100%> (ø)
app/services/themes/theme-core.ts	69.56% <100%> (+39.83%)	⬆️
app/services/themes/theme.service.ts	19.27% <20%> (-1.62%)	⬇️

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