refactor ManagedStorage for save get

[Sneezry]

The hard coded ManagedStorage.get default value false doesn't make sense. We also have keys with string values, and their default values should not be false.

[codecov]

Codecov Report

Merging #727 (4854efb) into dev (8c9beba) will not change coverage.
The diff coverage is 92.30%.

@@           Coverage Diff           @@
##              dev     #727   +/-   ##
=======================================
  Coverage   18.45%   18.45%           
=======================================
  Files          17       17           
  Lines        1523     1523           
  Branches      331      331           
=======================================
  Hits          281      281           
  Misses       1210     1210           
  Partials       32       32           

Impacted Files	Coverage Δ
src/models/storage.ts	21.81% <80.00%> (ø)
src/store/Menu.ts	50.00% <100.00%> (ø)

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