Properly use async/await in all areas it can be used in backend

[johnthagen]

Fixes part of #882.

Use async / await rather than .Result in all API methods to increase performance.

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This change is 

[imnasnainaec]

Reviewed 9 of 9 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[codecov-io]

Codecov Report

Merging #893 (1d3836c) into master (6bc23e1) will not change coverage.
The diff coverage is 81.25%.

@@           Coverage Diff           @@
##           master     #893   +/-   ##
=======================================
  Coverage   50.93%   50.93%           
=======================================
  Files         241      241           
  Lines        6601     6601           
  Branches      421      421           
=======================================
  Hits         3362     3362           
  Misses       2926     2926           
  Partials      313      313           

Flag	Coverage Δ
backend	56.15% <81.25%> (ø)
frontend	45.68% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
Backend/Controllers/UserController.cs	46.21% <0.00%> (ø)
Backend/Services/PermissionService.cs	0.00% <0.00%> (ø)
Backend/Services/UserApiServices.cs	0.00% <0.00%> (ø)
Backend/Controllers/UserEditController.cs	63.24% <100.00%> (ø)
Backend/Services/LiftApiServices.cs	93.34% <100.00%> (ø)
Backend/Services/UserEditApiServices.cs	100.00% <100.00%> (ø)
Backend/Services/WordApiServices.cs	86.07% <100.00%> (ø)

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