Validate input style based on source format

[chrismayer]

Currently there is only a minimal validation of the input style unrelated to the source format. This can lead to issues when having on matching parameter sourceFormat and content. For example when sending a JSON object and defining sourceFormat=SLD.

A more sophisticated validation based on sourceFormat and its content should be implemented.

[slafayIGN]

The described situation leads to a 400 return because the parsing of the input fails.

The only problematic situation is when the content is in a XML format and the sourceFormat is in another XML format.

For instance the input is a SLD file and the sourceFormat is set to QML. In this case the output will be an almost empty style but without any error raised (when targetFormat is different from sourceFormat). This is a really minor issues.