Fix "stop tracking on browser close" hook

[tcrammond]

Please remember the Contributing Guidelines ❤️

🌟 What does this PR do?

Tweaks the code to "detect when browser is closed, and stop the running entry". Removed a counting variable and moved everything into the window callback. Tried to await all the promises that happen so we have the best chance of our code being allowed to complete before the browser is gone.

Note: I couldn't reproduce the issue but it looked pretty likely that something could go wrong with it.

Also removed some dead code that was trying to do the same thing

🐛 Recommendations for testing

All changes should be tested across Chrome and Firefox.

• Enable the "stop automatically" setting
• Start a timer
• Close the browser
• Open the browser again and see that the entry was stopped ✅

Do you know or can you spot a better way to make this behaviour more reliable?

📝 Links to relevant issues or information

Fixes #1687. (Hopefully)

[lise-toggl]

I could not get this to work (also doesn't work on master) :(

It looks like on close listener doesn't trigger for me at all, could be a 🐧 thing. @shantanuraj can you try it out?