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

*.pyc
**/__pycache__
.vscode
**/build/**
*.class
**/.svghmithumbs/**
**/my_*.der
**/my_*.pem
tests/tools/Docker/requirements.txt
**/management.json
**/.secret

doc/_build/**
doc/locale/**

C_runtime/**/*.d
C_runtime/**/*.o
beremiz_runtime
**/tmp/**