Upload own data backend

[cephaschapa]

changes

• Adds migration to create userFile relation
• Adds userFile model class
• Adds file to user association in init-models
• Adds POST route to create a user file
• Adds GET route to fetch all user files
• Adds GET route to fetch a user file
• Adds DELETE route to remove a user file
• Adds file download route to enable downloading files of varying file types
• Adds unit test
• Adds helper functions to accommodate file creation to be used for unit tests
• Minor comments