Replace User class with EGUser across the codebase

This commit introduces the new `EGUser` class, which replaces the existing `User` class in multiple files, including `EnvelopeModel.vb`, `State.vb`, and `UserModel.vb`. The `EGUser` class extends `User`, adding new properties while maintaining existing functionality.

Key changes include:
- Updated property types from `User` to `EGUser` in relevant models.
- Method signatures in `UserModel.vb` modified to accept and return `EGUser`.
- Domain entities in `Envelope.cs` and `EnvelopeHistory.cs` now reference `EGUser`.
- Complete removal of the `User.cs` file.
- Added a new package reference for `UserManager.Domain` in the project file.
- Updated `MYUSER` variable in `ModuleSettings.vb` to use `EGUser`.

These changes enhance the user model to better meet application requirements.

EnvelopeGenerator.CommonServices/Models/EnvelopeModel.vb

@@ -37,7 +37,7 @@ Public Class EnvelopeModel
             .AddedWhen = pRow.Item("ADDED_WHEN"),
             .ChangedWhen = pRow.ItemEx(Of Date)("CHANGED_WHEN", Nothing),
             .CertificationType = ObjectEx.ToEnum(Of CertificationType)(pRow.ItemEx("CERTIFICATION_TYPE", CertificationType.AdvancedElectronicSignature.ToString())),
-            .User = New User(),
+            .User = New EGUser(),
             .ExpiresWhen = pRow.ItemEx(Of Date)("EXPIRES_WHEN", Nothing),
             .ExpiresWarningWhen = pRow.ItemEx(Of Date)("EXPIRES_WARNING_WHEN", Nothing),
             .ExpiresWhenDays = pRow.ItemEx("EXPIRES_WHEN_DAYS", 0),