Update webpack to latest 4.x

[ZakarFin]

This requires changes to scripts in applications with:

--env.appdef=applications -> --env appdef=applications

for any --env.[something]

Updated:

• webpack 3.43.0 -> 4.47.0
• webpack-cli 3.3.11 -> 4.10.0
• webpack-dev-server 3.8.0 -> 4.15.2

See:

• Update package scripts due to webpack-cli update sample-application#35
• Migration notes for frontend scripts oskari-server#1069