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

     1

input,smta,1,DINT,0

     2

input,smtb,1,DINT,1

     3

input,smtc,1,DINT,2

     4

input,smtd,1,DINT,3

     5

input,smte,1,DINT,4

     6

output,smtf,1,False,DINT,0

     7

output,smtg,1,False,DINT,1

     8

output,smth,1,False,DINT,2

     9

output,smti,1,False,DINT,3

    10

output,smtj,1,False,DINT,4