feat: add options panel

[AnsahMohammad]

Add options pane in the top-left with following options :

• update-interval-slider
• set transfer-pages
• set transfer-threads

This PR resolves #50

[AnsahMohammad]

Screenshot of the implementation :

[whimboo]

Thank you for your first PR! And sorry that it took a bit longer for me to check it.

Before I dig into all the changes I wanted to have a look how it actually works, but at least one of the changes is actually breaking the extension. Can you please check yourself? From the command line you can run npm run start:firefox -- --firefox=nightly to actually start a Nightly build with the webextension running. For me no values are displayed and certain actions like switching between pages, threads etc fails as well.

[whimboo]

Lets keep those comments that are not addressed with your PR.

[AnsahMohammad]

I assumed these comments referred to the boolean buttons we added here:

Since we're handling this logic in option.js, I thought they were no longer needed.

[AnsahMohammad]

Thank you for your first PR! And sorry that it took a bit longer for me to check it.

Before I dig into all the changes I wanted to have a look how it actually works, but at least one of the changes is actually breaking the extension. Can you please check yourself? From the command line you can run npm run start:firefox -- --firefox=nightly to actually start a Nightly build with the webextension running. For me no values are displayed and certain actions like switching between pages, threads etc fails as well.

Oops! It looks like the recent commit caused an "Assignment to constant variable" error. This also highlights the need to start adding tests to catch such issues early. Thanks for checking it!