Transfer js code in listeners.html into separate .js file

[Dalu46]

Fixes #1184 (<=== Add issue number here)

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[gitpod-io]

[TildaDares]

Amazing work @Dalu46. Thank you!!

[TildaDares]

Hi @Dalu46, can you resolve the merge conflicts? Thanks!

[TildaDares]

Hi @Dalu46, the closing body tag is missing. Thanks!

[TildaDares]

Hi @Dalu46, do you need help with this? Please reach out if you do!