Add new vars: $input-bg-focus and $input-color-focus

Created by: Mevrael

Now there are only 2 variables to style focused input:

$input-border-focus $input-box-shadow-focus

However, there are additional 2 variables to style input and there is no way to change those styles when element is focused:

$input-bg: $input-color:

Adding 2 new variables $input-bg-focus and $input-color-focus would fix this.