To be identical to the lower half of the skybox sides.
Now needed as the skybox base is often seen due to increasingly vertical
mapgens.

Add new colours 'skycolour_bright_night', 'bgcolour_bright_night'
and enable these between sunset end and sunrise start
Night sky has same hue as day sky but is darker and more saturated
Night horizon haze (bgcolour) is slightly less saturated and
slightly brighter than night sky, to be consistent with daytime
horizon haze

Top of texture no longer shows above horizon during night and day

* Sky: rename Box => m_box and inline getBoundingBox
* Uniformize aabbox3d<f32> to aabb3f

Move debug streams to log.cpp|h

Move GUI-related globals to clientlauncher

Move g_settings and g_settings_path to settings.cpp|h

Move g_menuclouds to clouds.cpp|h

Move g_profiler to profiler.cpp|h

Move texture_min_size even further down the pipe. Now, textures are JIT-upscaled using an image transformation, right at the time they're added to a mesh or particle; images used in 2D elements are left unscaled. This should fix any remaining issues with HUD elements.

Clean up nearby code a bit

As a small side effect, it is now possible to add a background texture
to the chat console by simply providing background_chat.jpg, it is no
longer necessary to also add "console_color =" to minetest.conf.

sky.cpp: m_bgcolor.getAlpha() was being used before initialised

mesh related: m_highlight_mesh_color was being used uninitialised

Add (experimental) support for topbottom as well as sidebyside 3d mode

Lessen the sky color glitch when quickly turning to look up after looking at ground that contains caves