Add transparent player spawn markers to KTX config

[liback]

Instead of the ugly scrags, add transparent player models as spawn markers.

• nQuake client (the local KTX server config, should be safe since we bundle a client version that supports it)
• nQuakesv (might require some more testing to see that nothing unexpected breaks in the wild?)

set k_spm_custom_model          "progs/player.mdl"  // specify which model to use for spawn point markers
set k_spm_color_rgba          "0 1.2 1.2 0.3" // specify RGB color and alpha for spawn model
set k_spm_glow                  0               // enable yellow glow for spawn markers (0 = off, 1 = on)
set k_spm_show                  1               // show spawn point markers (0 = off, 1 on)