build: Use https in submodule URL for external/xdg-file-dialog

refactor: Introduce Rust instead of boost dependencies

build: Change snap grade from devel to stable

fix: Missing zlib dep in msdfgen

doc: Fix some spelling/grammar in README

fix: Add expected location of oexserverd.exe to PATH

oesenc::ServerControl expects oexserverd executable to be in the
PATH. On Windows this is a non-standard path. This functionality broke
when it was moved from nautograf to oesenc.

feat(scene): Render depth contours

ci: Build release build, run cpack and upload ZIP content

Add "about" dialog with licensing information