TVB-2587: Separated the file saving and obtaining the temp folder to facilitate multi-file requests

TVB-2587: Added generic get_file_type method for uploaders

TVB-2587: Added generic get_upload_files_name method for UploaderViewModel

TVB-2587: Adapter importers to facilitate launch upload operation in TVB Rest

TVB-2587: Add TODO for Gifti parser

TVB-2587: Added new function to test if a file exists in the request because it is intented to be used in operation_resource as well now

TVB-2587: Extracted some duplicated code for handling the 2 data files of uploaders in handle_data_file

TVB-2587: Added extra code to support uploaders in launch_operation

TVB-2587: Corrected a few minor errors. Everything is fine now.

TVB-2587: Moved obtaining file types to view models, generalized obtaining file name with os.path.basename and added getattr instead of eval

TVB-2587: Extended launch_operation to client-side.

TVB-2587: Corrected this

TVB-2587: Removed unnecessary imports