[Umbrella] Text Editor Example

[ptziegler]

This items primarily serves to keep track of everything that is wrong with our Text Editor:

• IllegalArgumentException upon opening the editor

When the editor is openend, the following exception is logged:

java.lang.IllegalArgumentException: Offset: -1 is invalid
	at org.eclipse.draw2d.text.TextFlow.getCaretPlacement(TextFlow.java:257)
	at org.eclipse.gef.examples.text.edit.TextFlowPart.getCaretPlacement(TextFlowPart.java:82)
	at org.eclipse.gef.examples.text.tools.TextTool.getCaretInfo(TextTool.java:514)
	at org.eclipse.gef.examples.text.tools.TextTool$CaretRefresh.refreshCaret(TextTool.java:880)
	at org.eclipse.gef.examples.text.tools.TextTool$CaretRefresh.run(TextTool.java:869)

• Bold/Italics/Underline actions can't be undone

Selecting a bold text and clicking the "bold" action adds invalid elements to the model, rather than removing the bold element.