Self-shadowing and gl_lightmap additions

- Self-shadowing routines (no .glsl yet) which adds a new permutation.
- SHADERPERMUTATION_BOUNCEGRIDDIRECTIONAL moved to static parms.
- New cvars: r_glsl_selfshadowing, r_glsl_selfshadowing_scale,
r_glsl_selfshadowing_offsetscale, r_glsl_selfshadowing_lightmap,
r_glsl_selfshadowing_lightmap_scale,
r_glsl_selfshadowing_lightmap_offsetscale,
mod_noshader_default_selfshadowing, mod_q3shader_default_selfshadowing,
mod_q3shader_default_selfshadowing_scale.
- New shader keyword: dpselfshadowing
- Shadowmapping LOD now controlled by cvar r_shadow_shadowmapping_lod
(so it can be turned off).
- Added new modes to gl_lightmap. Fixed rendering of nodraw surfaces in
gl_lightmap mode.