Implement volume mesh inspection via slice planes (nmwsharp#129)

* basic geometry shader

* Transer

* Working slice planes

* working handshake

* Transitioning to full geometry shader

* quick commit

* Restructured to slice plane side and picking UI

* working :)

* Working level sets and slice materials

* Working Geometry Slice Planes and Level Sets

* Fix Compiler Warnings

* Fix Ground Plane Reflections

* Improved interface functions

* Improve edge rendering

* Added python functions and fixed edge rendering

* Add space between VolumeMesh

* Expose Level Set Functions

* Expose more Level Set functions

* Added: Support for Hex Meshes (converted to tet meshes when generating geom buffers)

* Improved: Hex Mesh support

* Quick Commit

* Fixed: Hex to Tets for slicing

* Improved UI

* remove cmake files

* return nullptr for empty structure

* use persistent values for slice plane options

* fix uint for windows builds

* more windows compile fixes, lazily populate tets

* refactor draw loop, fix include, more refresh checks

* change inspect menu to popup

* one more missing header

* more uint fixes

* rename slice --> inspect

* hide volume mesh level sets for now

* remove unused function

* add simple unit test

* refactor, add more defensive checks

* remove unused logic

Co-authored-by: Nicholas Sharp <nsharp@cs.cmu.edu>

show widget by default

better handling of view style in UI

set backend at runtime, hide windows on init, missing include (nmwsha…

…rp#50)

* set backend at init time

* glfw hide windows on init(), no focus on show()

* bugfix: missing include

* include Windows in CI

render backend overhaul, version 1.0.0