Manage the calls with "form-data" header

[Mystilund]

As express recommends, we can create connectors for some libs which already do the work.
Here are the libs recommended.

• https://www.npmjs.com/package/multiparty
• https://www.npmjs.com/package/busboy
• https://www.npmjs.com/package/formidable
• https://www.npmjs.com/package/multer

It avoids to create a new lib to do the same thing or to choose a library which can die (like formidable which is looking for maintainers)