### Purpose
Implement transparent background for Storm delegate
![image](/attachments/2e748faf-678a-4c91-b997-f3d8d416142b)
### Technical steps
Implemented STORM_HYDRA_RENDER_PT_film.
### Notes for reviewers
Should be reviewed with the pull request BogdanNagirniak/blender#71
Pull Request BogdanNagirniak/blender-addons#21
### Purpose
Make available Strom delegate to utilize for material preview.
### Technical steps
- Set attribute bl_use_preview to True.
Pull Request BogdanNagirniak/blender-addons#20
### Purpose
Engine creation for storm delegate has to be performed in `render()` function.
### Technical steps
Moved engine creation and syncing to `render()` function, made `update()` empty.
Pull Request BogdanNagirniak/blender-addons#17
### Purpose
For testing purposes it'll be useful to have possibility to render USD stage.
### Technical steps
1. Added `AddonPreferences` class with `dev_tools` setting.
2. Added `DevProperties` with USD render settings and `STORM_HYDRA_PT_dev` UI panel.
3. Added `StormHydraRenderEngine._sync_usd_stage()` to sync USD stage into render engine.
### Notes
Works with BogdanNagirniak/blender#49
Pull Request BogdanNagirniak/blender-addons#14