py_ext: fix CSV Writer

fix POU logic :
- SAVE is a BOOL
- invocation of py_eval on rising edge of SAVE
- remove save python argument

fix python:
- use no encoding for file open (python2)
- re-use detected dialect if any
- use no "rt+" and truncate since no need to re-sniff dialect for output file
- return "OK" instead of "#SUCCESS", preventing POU logic to ACK result
- support creating new line if writing just after last line
- support appending data on short rows

fix example:
- use a HMI:Button to trigger CSV write instead of HMI:Input +1
- reload CSVs on on each new CSV opened in file browser
- add display of CSV write output

#!/bin/bash

# Run python example throug command line, and check usual output

coproc setsid $BEREMIZPYTHONPATH $BEREMIZPATH/Beremiz_cli.py -k --project-home $BEREMIZPATH/tests/projects/modbus_test_tcp build transfer run;

while read -u ${COPROC[0]} line; do 
    echo "$line"
    if [[ "$line" == "TEST OK" ]]; then
        pkill -9 -s $COPROC_PID 
        exit 0
    fi
done

exit 42