Added support to MatCaps light shader

[Micheus]

This commit introduces MatCaps light shader support and reorganizes related modules. Several functions were moved to wings_image.erl for consistency, radio group options were added to wings_menu.erl, and shader light handling was extended to include MatCap. The View menu was updated to group display options under "Show" and redefine light modes with radio groups. New constants and uniforms were added to support MatCap textures, blending, and rotation. Additional shaders and textures were introduced to complete MatCap integration.

Files changed:

• plugins_src/primitives/wpc_image.erl: Removed local functions and switched to wings_image.erl implementations.
• src/wings_image.erl: Exported img_type/1 and nearest_power_two/1.
• src/wings_menu.erl: Added radio group support and select_item/1.
• src/wings_view.erl: Moved display options to submenu; redefined shader lights.
• src/wings.hrl: Added MATCAP_MAP_UNIT constant.
• shaders/standard.vs: Exported view info for matcap_light.fs.
• src/wings_light.erl: Initialized MatCap variables and load_matcap_texture/1.
• src/wings_shaders.erl: Added shader_light/1 and matcap_light program.
• src/wings_view_win.erl: Added MatCap option with texture, rotation, blending; updated light toggle handling and sync with View shaders.
• shaders/matcap_light.fs: New fragment shader to render MatCap light.
• shaders/hemilight.fs: Renamed to hemi_light.fs for naming consistency.
• textures/matcap/: Created subfolder with MatCap textures included in Wings3D distribution. All files are freely available online; readme.md added with more information.

NOTE:
Added support to MatCaps light shader. Thanks Flüfy Nũrbs

[Micheus]

[dgud]

The problem with the release needs to be fixed.
The easiest would be to fix:
Change ["textures",""] to use a file extension filter like ["textures",".{png,bin}"]

But you need make a release and check the release that everything is included and that the release works.