Back ported skybox shader, material and integration into Background rendering.
Originally written by Salwan for Paragon.
Compiling and running on Linux
Removed the ub*.dds skyboxes from paragon.
The default is actually one of them and will need replacing eventually.
Fixed up the code to use a default and to use cubemaps from a mod named "ub*.dds" automatically.
Add some draw flags so we can enable or disable various states depending on player preferences.
Draw only the skybox.
Updated the default cubemap to be more Pioneer-esque.
Fix the default constructor!
Merge branch 'master' of github.com:fluffyfreak/pioneer into skybox

Conflicts:
	src/Background.cpp
Enable and disable the star for hyperspace.
Fix incorrect indexing of cubemaps.
Merge branch 'skybox' of github.com:fluffyfreak/pioneer into skybox
Merge remote-tracking branch 'fluffyfreak/skybox' into skybox
silence init order and signed comparison warnings
Fix the conversion back to 0.0 to 1.0 range from 0-255 Uint8
Move the skybox from cube to skybox folders.
Remove the non-DDS cubemap loading codepath.
Use std::unique_ptr instead of raw pointers.
Change the way the default cubemap is loaded during initialisation.
cache the default cubemap, use stringf for formatting the loading of mod based cubemaps.
Spelling corrections and style renaming etc.
Simplify test.