Add admin role and user management

[VMelnalksnis]

Changes proposed in this pull request:

• Add administrator role
• Add initial admin user
• Add ability users in the administrator role to disable user accounts
• Show unreleased changes in changelog

[codecov]

Codecov Report

Merging #785 (3207270) into master (47020bb) will increase coverage by 0.43%.
The diff coverage is 80.72%.

@@            Coverage Diff             @@
##           master     #785      +/-   ##
==========================================
+ Coverage   73.74%   74.17%   +0.43%     
==========================================
  Files         329      337       +8     
  Lines        9471     9611     +140     
==========================================
+ Hits         6984     7129     +145     
+ Misses       2487     2482       -5     

Impacted Files	Coverage Δ
...e/Gnomeshade.WebApi/Areas/Admin/Pages/Index.cshtml	0.00% <0.00%> (ø)
...nomeshade.WebApi/Areas/Admin/Pages/Index.cshtml.cs	0.00% <0.00%> (ø)
...eas/Identity/Pages/Account/ExternalLogin.cshtml.cs	13.46% <ø> (ø)
...ebApi/Areas/Identity/Pages/Account/Login.cshtml.cs	74.28% <ø> (+34.28%)	⬆️
...reas/Identity/Pages/Account/LoginWith2Fa.cshtml.cs	30.76% <ø> (ø)
...tity/Pages/Account/LoginWithRecoveryCode.cshtml.cs	34.28% <ø> (ø)
...pi/Areas/Identity/Pages/Account/Register.cshtml.cs	27.27% <ø> (ø)
...n/StartupFilters/DatabaseMigrationStartupFilter.cs	100.00% <ø> (ø)
...ade.WebApi/Areas/Admin/Pages/Users/Index.cshtml.cs	69.44% <69.44%> (ø)
...iguration/StartupFilters/AdminUserStartupFilter.cs	75.36% <75.36%> (ø)
... and 12 more

... and 3 files with indirect coverage changes