Add ui scale factor

[andrewdavidmackenzie]

Fixes #747

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 27%. Comparing base (684a2b2) to head (9ce1b08).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
src/views/layout_menu.rs	0%	7 Missing ⚠️
src/piggui.rs	0%	5 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##           master   #812   +/-   ##
=====================================
- Coverage      27%    27%   -0%     
=====================================
  Files          46     46           
  Lines        6060   6064    +4     
=====================================
  Hits         1631   1631           
- Misses       4429   4433    +4     

Flag	Coverage Δ
unittests	27% <0%> (-<1%)	⬇️

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