Change work with documents to multipart-form-data requests in the api (seems like Scalatra limitation)

[manonthegithub]

During development I found out that I am using the Scalatra in a bit non expected way when uploading documents, so to support binary data and really large files (or big load), we will have to change the api again for /document/save. we will need to use multipart form data parameters (that is how it is supposed to work with files in Scalatra..., I may investigate bit more on that, but looks like that). This won't be a major change in the code, but will affect api (using multipart instead of classic post).