Attempted to introduce Top Bar bottom margin settings and feature

[atimeofday]

Tentative solution for Issue #88.

This should maintain identical default and current behavior, while introducing two new settings to toggle and adjust a slider for a separate bottom margin value of the Top Bar, for personal preference or compatibility with other extensions such as Forge.

These changes work on my end (so far), but I am rather new to Gnome extension development, so please do double check whether each change is necessary, correct, complete, and properly formatted.

Before:

After:

New Bottom Margin settings:

[neuromorph]

Hello,

Thank a lot for your PR, appreciate it!
I glanced through it and it looks like you have properly handled the stylesheets and prefs 👍
Some work will be needed for handling WMax bar and Bar in bottom position. And more testing of course :)
I will merge it now and then work on further updates.
Since you are already using it, if you have found any issues, let me know I will get it sorted.
I will release an update soon, once things are in place.

Thank you, again!