Update to work with node.js v16 LTS

Redis:
- redis-> redis@v3 until v4 is working stable
  ( tj/connect-redis#336 )
- connect-redis -> 6.0.0
- update @types/connect-redis -> ^0.0.18 and removed
  @types/redis since this is not necessary anymore

Corrected edumeet server version

deactivated spdy since it is not working anymore with node.js>15
( spdy-http2/node-spdy#380 )

removed package-lock.json ( just support yarn, use npm at your own risk