Upgrade version of EcmaScript

[fflorent]

Currently we use the version 2017 of EcmaScript.

Dmitri suggested it should be safe to upgrade EcmaScript to version 2019. Quoting him:

I checked throug caniuse statistics, and it's well-supported for the last 3 years of browser versions.

Maybe we could upgrade to an even newer version for node js.

Not a high priority issue though and after an attempt, there are some cascading issues to address.

Some references to the ecmascript versions I noted:

• in tsconfig files
• in .eslintrc
• in webpack config files