refactor core.py

convert reference ids to ObjectIds

when receiving a project id for a session or a session id for an
acquisition convert them to ObjectIds

closes #154

Add some more job stats

closes #147

create jobs for each file received by the engine

Input schemas

closes #141

changed the json schemas for label in acquisitions, projects, sessions

remove filetype and mimetype

correct input json schemas
closes #132

use matched_count for returned status code

closes #103

identify mimetype at download time

include algorithm in hash

implement advanced path calculation in downloads

Job tags

Multiple files upload