Seperate client and server of FTP (#1106)

* added sample file to transfer

* split client and server into separate files

* client and server now work in python2

* server works on python3

* client works on python3

* allow configurable ONE_CONNECTION_ONLY for testing server

* allow testing of ftp server + client

* use f-strings

* removed single letter vars

* fixed bad quote marks

* clearer file handler names

* 'with open() as' syntax

* unicode and emojis in the test data

* s -> sock

* consistent comment spacing

* remove closing formalities

* swap in and out_file

* f-string

* if __name__ == '__main__':