* The Publisher is all hooked up. No native Save File dialogs yet, so
uses the dev shell Prompt() to ask for output filename.
* Custom-only or builtin doodads too can be stored in the level's file
data, at "assets/doodads/*.doodad"
* When loading the embedded level in the Editor: it gets its custom
doodads out of its file, and you can drag and drop them elsehwere,
link them, Play Mode can use them, etc. but they won't appear in the
Doodad Dropper if they are not installed in your local doodads
directory.
* Fleshed out serialization API for the Doodad files:
- LoadFromEmbeddable() looks to load a doodad from embeddable file
data in addition to the usual places.
- Serialize() returns the doodad in bytes, for easy access to embed
into level data.
- Deserialize() to parse and return from bytes.
* When loading a level that references doodads not found in its embedded
data or the filesystem: an Alert modal appears listing the missing
doodads. The rest of the level loads fine, but the actors referenced
by these doodads don't load.
