fixes #270

- Fix a memory leak where a layout was created without being used.
- Fix uninitialized value.

The color scheme of nheko obeys the default color theme of Qt
(i.e. the system theme). It uses a Qt stylesheet to accomplish this,
which means replacing the color theme with a custom theme would only
be a matter of writing a new style sheet and loading it into the app.

Fixes #95

Basically reverts the last font related commits since pointSize isn't
as reliable as pixelSize.

Also some layout values (margins, spacings) have been moved out to Config.h.

[ci skip]

- Minor refactoring

- Add border width on Badge