Improve Editor Feedback to the User in Case of Wrong EATXT Files

[joerg-holtmann]

There are some situations in which the user can type in text that does not adhere to the EATXT grammar and the editor does not report this sufficiently back to the user. More specifically:

• There are no red error markers directly in the text file. I think that this has something to with the whitespace-aware language, as normal bracket-style languages do not have that problem, as far as I know.
• Some of the error messages are not understandable, like some messages from the parser (e.g., "EOL expected").

[Wilson008]

Temporarily close it, once we found somewhere else needs to be improved, then open it.