gewf and autodetect which connector to use

[jocelyn]

about experimental gewf:

• We should maybe try to have a better way to identify at run-time which connector should be used.
• for now it is based on executable file name and extensions.

Maybe some environment variables are present at run-time that would help.
But once again the "gewf" tool is experimental and the generated code should also generate a HowTo documentation...