activate (nearly) all SonarQube rules and fix the issues

[lg2de]

No description provided.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@c0aade4). Click here to learn what that means.
The diff coverage is 85.02%.

@@            Coverage Diff            @@
##             master      #31   +/-   ##
=========================================
  Coverage          ?   87.81%           
=========================================
  Files             ?       32           
  Lines             ?     2560           
  Branches          ?      384           
=========================================
  Hits              ?     2248           
  Misses            ?      240           
  Partials          ?       72           

Impacted Files	Coverage Δ
...ccounting/Presentation/CloseYearDesignViewModel.cs	100.00% <ø> (ø)
...impleAccounting/Presentation/DataGridExtensions.cs	0.00% <0.00%> (ø)
...SimpleAccounting/Presentation/MessageBoxWrapper.cs	0.00% <ø> (ø)
src/SimpleAccounting/Presentation/RelayCommand.cs	75.00% <ø> (ø)
src/SimpleAccounting/Presentation/ShellView.xaml	0.00% <ø> (ø)
src/SimpleAccounting/Reports/ReportBase.cs	100.00% <ø> (ø)
...Accounting/Presentation/ImportBookingsViewModel.cs	59.47% <28.07%> (ø)
.../SimpleAccounting/Presentation/AccountViewModel.cs	81.81% <66.66%> (ø)
...rc/SimpleAccounting/Presentation/ShellViewModel.cs	89.75% <88.03%> (ø)
...rc/SimpleAccounting/Reports/AnnualBalanceReport.cs	91.33% <91.30%> (ø)
... and 46 more

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