Added a new control (ErrorView) for displaying error-messages.
Replaced the ErrorTextBox in EditorForm with an ErrorView.
Added four columns to the ErrorView.
Overridden the OnSizeChanged method in ErrorView to ensure that the descriptionheader takes up as much space as possible.
Implemented the AddError method in ErrorView.
Implemented a handler for when an error is selected in the ErrorView control.
Added a CodeTextBox property to the ErrorView such that selecting an error will show the error in the CodeTextBox.
The column headers ErrorView in EditorForm are not clickable.
If an error at EOF is selected, the codetextbox goes to EOF.
Added an enum for denoting different types of compiler errors, as per #8.
Added the ErrorType to the CompilerError.
Added methods in ErrorManager for adding errors with different error types (as defined by ErrorType). This closes #8.
The CompilerExecuter in SablePP.Compiler halts validation only when at least one of the errors has errortype 'Error'.
Merge branch 'ErrorListView' into branch 'Warnings'

Conflicts:
	SablePP/SablePP.Tools/Editor/EditorForm.Designer.cs
Added an 'info' icon to MessageIcons in SablePP.Tools.
The ErrorView handles the three different error types using different icons.
Created a nested type in ErrorManager for handling collections of errors.
Added three ErrorCollections to the ErrorManager, one for each error type.
Added warning and message squiggly lines to the CodeTextBox.
Added VisitInParallel methods to the ReturnAdapter for two and three arguments.