Fix/wallet icon

[ryuash]

Description

Changes:

• I decided to change the FlatButton in to a flat GradientButton just so we would have less inconsistencies with the widget type changing between themes.

Checklist

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

[codecov[bot]]

Codecov Report

Merging #134 into master will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #134      +/-   ##
==========================================
- Coverage   61.90%   61.88%   -0.03%     
==========================================
  Files         266      266              
  Lines        6744     6740       -4     
==========================================
- Hits         4175     4171       -4     
  Misses       2569     2569              

Impacted Files	Coverage Δ
lib/ui/theme/colors.dart	86.66% <100.00%> (+11.66%)	:arrow_up:
lib/ui/widgets/buttons/primary_button/index.dart	100.00% <100.00%> (ø)

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