Canonical representation in cd

Current directory is now displayed canonically in instruction.
- cd
Translated ParseException messages into English

Error messages for wrongly used instructions are now displayed in
English.
Refactoring for the messages.
Deleted TODO task for last commit
Fixed download + upload  |  Added use of error stream  |  English as output language.

Now available for full testing.
Download also skips bytes if the downloaded file cannot be written
(prevents asynchonous behavior Server <-> Client)

Use of error stream implemented.

Unified output language (English).