UI and UX improvements

[RiccardoM]

Description

This PR implements various UI and UX fixes. Particularly:

• Fixed the visualization of posts' times (fixes #57)
• Improved the post message visualization (fixes #69)
• Improved the wrong recovery password (fixes #70)
• Added the read check inside the view mnemonic screen (fixes #71)
• Improved the edit of the account (fixes #74)
• Improved the font visualization on iOS devices (fixes #76)

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.
• [x] Added an entry to the CHANGELOG.md file.
• [ ] Re-reviewed Files changed in the Github PR explorer.

[codecov[bot]]

Codecov Report

Merging #75 into master will decrease coverage by 0.19%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
- Coverage   17.75%   17.56%   -0.20%     
==========================================
  Files         254      256       +2     
  Lines        6177     6247      +70     
==========================================
  Hits         1097     1097              
- Misses       5080     5150      +70     

Impacted Files	Coverage Δ
lib/ui/blocs/mnemonic/mnemonic_bloc.dart	0.00% <0.00%> (ø)
lib/ui/blocs/mnemonic/mnemonic_event.dart	0.00% <ø> (ø)
lib/ui/blocs/mnemonic/mnemonic_state.dart	0.00% <0.00%> (ø)
.../ui/blocs/restore_backup/restore_backup_state.dart	0.00% <0.00%> (ø)
lib/ui/localization/export.dart	0.00% <0.00%> (ø)
.../screens/login/restore_mnemonic_backup_screen.dart	0.00% <0.00%> (ø)
...ens/security/security_login_biometrics_screen.dart	0.00% <0.00%> (ø)
...reens/security/security_login_password_screen.dart	0.00% <0.00%> (ø)
lib/ui/theme/fonts.dart	0.00% <0.00%> (ø)
lib/ui/theme/theme.dart	0.00% <0.00%> (ø)
... and 9 more

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