- Added parameterless and user-initializing constructors to `EGUser`.
- Removed unnecessary `using` directives and `#if NETFRAMEWORK` from `EGUser.cs`, `Envelope.cs`, and `EnvelopeHistory.cs`.
- Replaced `EGUser` property with `User` in `Envelope.cs` and `EnvelopeHistory.cs`.
- Retained default value for `CURRENT_WORK_APP` in `Envelope.cs`.