#66 refactor theme and utils in ui

[ryuash]

Description

closes #66

Checklist

• [x] Targeted PR against correct branch.
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• [ ] Wrote unit tests.
• [x] Run flutter format.
• [ ] Updated the documentation.
• [ ] Added an entry to the CHANGELOG.md file.
• [x] Re-reviewed Files changed in the Github PR explorer.

[codecov[bot]]

Codecov Report

Merging #67 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #67   +/-   ##
=======================================
  Coverage   17.76%   17.76%           
=======================================
  Files         254      254           
  Lines        6174     6174           
=======================================
  Hits         1097     1097           
  Misses       5077     5077           

Impacted Files	Coverage Δ
lib/ui/theme/theme.dart	0.00% <ø> (ø)
lib/ui/utils/extensions/user_ext.dart	85.71% <ø> (ø)
lib/ui/utils/icons/icon_data.dart	0.00% <ø> (ø)
lib/ui/utils/jazzicon/jazzicon_painter.dart	0.00% <ø> (ø)
lib/ui/utils/keys/export.dart	0.00% <ø> (ø)
.../widgets/post_content/header/post_item_header.dart	0.00% <ø> (ø)

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[ryuash]

(this isn't for the 4018 release!)

[ryuash]

don't touch this until #75 is merged~ there will be conflicts