editor: tile paint and collision strokes are one undo step, no collision option for tiles (visual-only model copy in the build), freed gl buffers and stale pick ids, export level as gltf/glb with textures and vertex colours

src/main/resources/com/eliasmueller/llamamod/editor/tools/help/context-help.txt

@@ -123,6 +123,7 @@ action.geo.deathPlane = 06-geometry.md#death-floors-and-the-death-plane
 action.geo.reimport = 07-meshes.md#re-import-mesh
 action.geo.libSave = 07-meshes.md#saving-to-the-library
 action.geo.exportObj = 07-meshes.md#export-selection-as-obj
+action.file.exportGltf = 07-meshes.md#export-the-level-as-gltf
 action.geo.* = 06-geometry.md#rotating-scaling-and-mirroring
 action.tex.manager = 08-textures.md#texture-manager
 action.tex.replace = 08-textures.md#replacing-pixels