Align MultiPart request parsing in Automation and Batch upload (WebEngine)

We parse MultiPart request in 2 different ways:

• In Automation, it uses MultiPartRequestReader and MultiPartFormRequestReader classes, which use javax.mail.*.
• In Batch Upload (and WebEngine), it uses FormData, which use Apache Commons Fileupload.

We have an issue on the filename, when it contains other characters than the one in US-ASCII.

Commons Fileupload reads correctly encoded filename in the header, as it uses UTF-8 encoding by default.

However, javax.mail seems to fail at it, it cannot decode correctly the filename. To make it correctly decode the filename, we should use {{ filename*=UTF-8''}} in the part header:

...
form-data; name="file"; filename*=UTF-8''blablaéèôûü__.txt
...

Browsers (at least Chrome and Firefox) send only filename in the part header:

...
form-data; name="file"; filename="blablaéèôûü__.txt"
...

=> We should probably align all the code to use Apache Commons Fileupload to parse MultiPart requests, and make sure we send correctly encoded part headers.