Refactor receiver handling and update solution structure

- Updated `BaseController.vb` to use `Receiver.Id` for deletion.
- Changed `Receivers` property in `frmEnvelopeEditor.vb` to `BindingList(Of ReceiverVM)` and adjusted initialization and usage throughout the file.
- Modified `frmFieldEditor.vb` to use `List(Of ReceiverVM)` for receivers and updated related methods.
- Adjusted color assignment logic in `frmMain.vb` to utilize a new `Value` class.
- Added new project for `EnvelopeGenerator.Form` in the solution file.
- Introduced new enums `ContractType` and `PageOrientation` in their respective files.

EnvelopeGenerator.Form/Controllers/BaseController.vb

@@ -76,7 +76,7 @@ Public MustInherit Class BaseController
             End If
 
             Dim oResult2 = pEnvelope.Receivers.
-                Select(Function(r) ReceiverModel.Delete(r.Id, pEnvelope.Id, oTransaction)).
+                Select(Function(r) ReceiverModel.Delete(r.Receiver.Id, pEnvelope.Id, oTransaction)).
                 All(Function(r) r = True)
 
             If oResult2 = False Then