spearmint: Rename more client to player in botlib and g_public.h
spearmint: Fix demo playback

Seek using correct file handle and fix handling seek error.
spearmint: Allow VMs to decide expected size of entity state network data

This would be required for supporting older demos with less entity state fields.
spearmint: Replace G_SET_BRUSH_MODEL with G_GET_BRUSH_BOUNDS

Most of SV_SetBrushModel can be done in Game VM, so move it there.