Migrate UI contribution to ES Modules

In order to match the current Web UI stack and needs, but also to understand what kind of challenges other contributions and addons may face, we should try to migrate the existing Aspera Connector code (on the UI side) to ES Modules and relying on actual npm dependencies instead of just believing that those will be available on Web UI.

This would allow us to perform proper validation to the code, to setup a proper unit test approach, to probably get some IntelliSense on our IDEs, to have more control on the dependencies we need, among other benefits.

For this we should also keep in mind that we'll need a proper bundling process which could also happen on UI loading performances since it is expected to minify instead of having every file available and loaded.