The basic featues of CommandEntry work

CommandEntry is usable, but not everything works as of yet:
- SyntaxHighlighting is crippled. It does not work in Maxima, but
in Qalculate some things are highlighted.
- Completion does not work, because Tabs are not recognised.
- The WorksheetTextItems do not look nice: They have a wierd border,
and the cursor is not shown.
- WorksheetTextItems are also too small, they should fill the whole
line.
- Cursor movement does not work for additional information blocks.
But I am not sure whether one should be able to navigate out of
those, as any modification outside should abort the evaluation
and destroy the additional information.
- There most certainly is more.
Other Entries can not yet be added to the Worksheet.