setting required env variables for local mode

[jmilkiewicz]

Fixes possibilty to run lighter in local mode. Till now env variables like:

• PY_GATEWAY_PORT
• PY_GATEWAY_HOST
• LIGHTER_SESSION_ID were not passed to shell_wrapper.py

This PR does not solve the problem of:

• setting custom env variables on session creation
• setting custom env variables on statement creation

[jmilkiewicz]

More context can be found #682