Refactor Profile and ColorScheme

Summary:
There's no point in returning null if we have a default
and we would check for null and query for the default
in all cases that we used it.

Export the private header ColorScheme

It's going to be used from Parts and App

Add ColorScheme() to the Profile

The profile used to hold the ColorScheme name, but if you
want to query for the ColorScheme you had to call ViewManager
but there's a class ColorSchemeManager that ViewManager used to call

Just make things simple:

• Profile has a colorScheme that it queries from the ColorSchemeManager
• Use profile->colorScheme() when you wanna something from the

colorScheme at the profile.

Reviewers: Konsole, hindenburg

Reviewed By: Konsole, hindenburg

Subscribers: konsole-devel

Tags: Konsole

Differential Revision: https://phabricator.kde.org/D13854