Improve the style of tabs

[RazinShaikh]

I find the default style of pyqt tabs quite dated. Customize the style by adding a stylesheet.

Few suggestions:

• make the tab area larger and more easily clickable
• only show the "x" to close when you hover over the tab; and choose a better colour than orange.
• make tabs be equal width

[boldar99]

Just so you know, on mac it looks quite different:

[RazinShaikh]

Better than windows but still not pretty 😅