New Torrust brand colors theme

[mario-nt]

I think it is worth considering the possibility of adding a new theme to the index GUI with the new branding colors, it is a really bold color but I think it kind of works, with a little adjustments to the saturation it should be less straining to the eye. Besides, we can keep the old orange as a "retro" or "classic" Torrust theme.

Some screenshots with quick mockups:

[mario-nt]

@josecelano @cgbosse @da2ce7 @grmbyrn

[josecelano]

I think, it would be fine to have a similar look, but I don't think it's necessary to "force" the same style between the org website and this app style. A style could be convenient for a website but not for a webapp. If it's possible and applying the same style doesn't impact usability, I would do it, but I would not spend time on that. I think it would be more beneficial for users to customize the app. In fact, many users have requested that feature. Ultimately, end users don't care about Torrust style; they usually want to apply their own.