cleanings, pictures and spell check

- ADD: pictures can be inserted from clipboard now
- ADD: spell check for AvalonEdit controls (thx to Chandramouleswaran
from CodeProject!)
- CHG: cleanings
namespaces and editors

- FIX: Euro chars
- CHG: moved TMEditorHelper to sub namespace
ribbon, messages boxes, redo/undo and spell checking

- ADD: UNDO and REDO feature
- ADD: more messagebox message
- DEL: picture output format and max size ribbon comboboxes
- FIX: deactivated SpellingErrorColorizer otherwise inline pictures do
not work e.g.