Passing the link of empack_env_meta.json file

[AnastasiaSliusar]

This PR is the part of the solution of https://github.com/QuantStack/qs.ai/issues/28 It includes next changes:

• a new plugin that takes empack_env_meta from search url params and this parameter contains a link where empack_env_meta.json file is hosted.
• This link is passed xeus-python during initialization of each kernel.

It should be used with https://github.com/emscripten-forge/pyjs/pull/74 together

[trungleduc]

CI is green!