fix: Vim theme parser and right color scopes

[Brayan-724]

Vim theme

Vim theme has been parsed wrong, before this pr it was using bg as fg and vice versa, now it is correctly setted.
Before, when creating the theme is needed to have bg and fg in Normal highlight, but someone that doesn't want to set
it and just use the default colors (fg: #FFFFFF, bg: #000000) can't use this. Now, fg and bg fallbacks to the
default colors mentioned before.

Syntax scheme

There're a few colors that are linked wrong taking nvim from reference.

struct A;
// ^

This is highlighted with StorageClass. This means to a class (A), but it should be a Keyword.
There's repeated storage scope, is in StorageClass and Type, now it is only in Keyword

[SergioRibera]

LGTM!