Fix quotes in french translation

This is RI0's french translation of robopaint. The quotes are not all normal double quotes so I replaced them all with normal double quotes. I am working on verifying and editing this translation.
"Paintbrush on a Snail" does not translate to "Escargot". I am not trying to "steal" your work as @techninja falsely (said)[https://github.com/evil-mad/robopaint/issues/159#issuecomment-61911981]. I will also note that some of the quotes you have used are not normal quotes and are curly quotes.