Support for multi-file input!

New features

• adds support for models which need more than one input to perform predictions
  • the REST API accepts a JSON with an arbitrary number of keys containing a fileurl and a matching format each
  • the Python API accepts single files, JSON files with multiple input paths and dicts with the same structure as the JSON files
  • stability improvements for both APIs: the REST API can now recognize more file types for downloads
  • the schema for the config now has a new format to support the multiple inputs

Other changes

• the test cases have more coverage
• the documentation was updated to reflect the new schema, multi-inputs and the PyPi package for the start script

Stability improvements and bugfixes

• Removes frontend from modelhub framework and relies solely on react app
• Removes netron from modelhub engine and relies solely on serving model visualizations through netron url
• Adds python package
• For numpy model outputs, returns url to h5 file in newly created output folder
• Addresses test errors