Lock down ProgramData\ManagedNotifications, and report dialog results in local time

[rodchristiansen]

What

1. Data folder ACL. %ProgramData%\ManagedNotifications kept ProgramData's inherited ACL, so Users could create and write files there. It now gets its own:
   • Root: owner SYSTEM; SYSTEM and Administrators full control; Users read and execute; inheritance off (O:SYG:SYD:PAI(A;OICI;FA;;;SY)(A;OICI;FA;;;BA)(A;OICI;0x1200a9;;;BU)).
   • logs only: the same plus Users modify (0x1301bf). dialog.exe runs in user context and appends to and rotates csharpdialog.log there, so this subfolder needs the write grant. The root never gets one.
   • MSI: PermissionEx on two permanent CreateFolder components, so an uninstall keeps the logs. .pkg: the postinstall applies the same DACLs with Set-Acl.
2. Local time. The WPF dialog set DialogResult.Timestamp to DateTime.UtcNow; the console path and the class default use DateTime.Now. The Timestamp: line on stdout, which the Run tab shows, is now local time.

Verified

• dotnet build, plus dotnet test: 25 passed.
• build.ps1 -Build -Msi -Pkg -Runtime win-x64 builds. The MSI's MsiLockPermissionsEx table has rows for both folders.
• Ran the generated postinstall ACL block against a scratch folder. Read-back DACLs: root D:PAI(A;OICI;FA;;;SY)(A;OICI;FA;;;BA)(A;OICI;0x1200a9;;;BU), logs ...(A;OICI;0x1301bf;;;BU).
• Not installed on a machine here. The ACL on a real install still needs checking in a VM.