Fixes #2

[samly97]

"npm run build" works out of box

Fix "npm run start"

• updated webpack to 4.44.1
• updated "react-dev-utils" to 6.0.0

Above breaks "npm run build" ...

Following changes are to get both commands to work

• the other dependency updates were to get "npm run build" working again
• replace unused UglifyJs webpack plugin with TerserPlugin
• modified InterpolationHtmlPlugin to reflect how it works with webpack 4.44.1
• replaced "contentHash" with "hash" as contentHash clashes with webpack definition