Rework and fix map rotation listing.

The current map is highlighted in green and prefixed with ‣.
The next map is shown inline and highlighted in yellow.
Map rotation entry numbers are displayed in white.

Maps not part of the rotation are shown inline but unnumbered.
This means that you could see (colours indicated by comments):

   4 plat23-b9
‣    atcshd                       // green
     nano                         // yellow (g_nextMap)
   5 arachnid2

Display of conditional items has been implemented.
If g_nextMap is set and valid, the next (in-rotation) map would be skipped. Fix this.
Remove nextmap colouring; always list the current and next maps.
Add a note about means of death enum & strings.
Add inverse dlight shadows for players and/or buildables.

Can be switched on or of with cg_playerShadows and cg_buildableShadows.
Cleanup BuildGPUShaderText()
Fix compile
Make shadows always gray.
Tidy & fix Unicode → UTF-8 conversion.
Fix GLSL compilation when rim lighting is enabled. (Typo.)

This was broken in commit 8883393a.
renderer: remove support for *very* old graphic cards
Refactor light tessellation
Use IterateLights() in more places
Fix potential NULL deref
Make sure the contents of tess are cleared before leaving RB_RenderInteractions*

Tess_StageIteratorLighting and similar use backEnd.currentLight to get the current light being rendered.
This is cleared to NULL later on, so make sure we finish before then.
fix invalid ptr deref
Clear the tess struct when finished in RB_RunVisTests
renderer: delete legacy renderer entity types (railgun, splash, ...)
renderers: we did not actually delete RT_BEAM

It is still used by cgame when the entity has eType ET_BEAM.
Althoguh no entity use it now we might want to keep it for later.
rendererGL: remove all stub D3D10 support