- Accumulate extension info while deserializing JSON
- Install extensions (if any) before installing target(s)
- Merged 'install' steps of the "add sprite" and "load project" paths
If the `dataFormat` field is absent, fall back on the older `assetType`
field. That can at least help us tell if something is a vector or bitmap
image, though it doesn't tell us which kind of bitmap.
When importing a project we know the file extension for each asset to be
loaded. This change provides that information to the storage system so
that we can load assets which don't use the default. For example, this
allows loading JPG-format backdrops.
In support of this change, there's a new function on `StringUtil` called
`splitFirst`, which splits a string on the first instance of a separator
character. This change includes unit tests for this new function.
