This reverts commit 148fffb0.

OpenGL_vertex:
* bufferize a duplicate calcul
* Factorize vertexes

This fixes biome surface in tunnels

Lua-api.txt: Document that paramtype='light' results in light propagation with attenuation and is essential for a light source to spread it's light

Revert "Switch default scaling factor to 0.75 as most ppl seem to have 96dpi screens instead of previous assumed 72"
which ain't required any longer as fonts are no longer autoadjusted
This reverts commit 7ad17a25.

Set builtin formspecs to autoscale in order to get consistent formspec look and feel
Uncouple label positioning from font size (May break some formspecs but is required to allow manual font adjustment)

Split gui_scaling to gui_scaling + hud_scaling as those elements need different handling on some devices

See issue #2017
Applied kahrl's gist

Switch default scaling factor to 0.75 as most ppl seem to have 96dpi screens instead of previous assumed 72