Added upload of samples into existing project.

Added UploadSamplesMixin, and use it for HTML POST with /project/{projectid}/upload in ProjectUpload, and for API POST with /api/v1/project/{projectid} in ApiProject.

Got rid of obsolete upload.py file.
This is only here to avoid reading the lines further ahead if we met 10 errors, right ? But since no samples will be added if there's even one error, shouldnt that take place as soon as one error is met ?