Convert Color4f usage to Color4ub where appropriate

I have made the changes to the code as suggested in the issue https://github.com/pioneerspacesim/pioneer/issues/2327

The main change was in Color.h to switch `typedef Color4ub Color`

I then checked all the files where Color is used and made appropriate changes.

There are some instances where there is some floating point math involving color calculation. I have left most of these instances alone. If they are to be changed I suggest it is done in a separate change.
I am including a list of places where there is such calculation or the places where I feel someone should check if the changes I made having a negative effect:
`text/TextureFont.cpp:   TextureFont::AddGlyphGeometry   VertexArray.Add`  Text is working, but maybe it still deserves a look.
`/graphics/gl2/Uniform.cpp:  Uniform::Set(const Color &c)`
`scenegraph/staticGeography.cpp: void StaticGeometry::DrawBoundingBox(const Aabb &bb)`
`Sfx.cpp:   Sfx::Render` smoke double calculations.
`Ship.cpp:` a lot of double calculations.

To test my changes, I have tried the following things:
- started on Earth, New Hope, checked various menu options (bulletin board, market, etc), and took off
- tried firing weapons (couldn't fire a missile :)
- visited Saturn to see the rings and flew in Venusian atmosphere
- I tested the hyperspace jump and the tombstone :)
- model viewer appears to be working

Please review.