Implement chunk upload

Add MultipartUploadService. It is used to upload files larger than 50 MB. Add HashService which is used to generate the hash for a file.

When the zipped project is bigger than 50 MB we often receive ECONNRESET error as such big file cannot be uploaded. So we upload it by chunks by using the server api. The file is validated with its hash, so we calculate it and send it to the completeUpload call. Currently the server does not verify each chunk hash.

Add tests for MultipartUploadService and HashService.
Judging from the code, these are implementation detail for the service and are not supposed to be changed by the code using this service. Therefore, they should not be part of the public interface. 

If you need them for testing, you can use dependency injection or simply hack them :)