investigate making resources import per file instead of flattening into one list

[shdwcat]

Currently all imports get flattened into one master resources table per document. This means all resource names must be unique or there might be conflicts, and that resources used just for a specific file (such as a widget) pollute this global namespace.

Ideally resources should work more like WPF, where resources are scoped to the file that uses them.

[shdwcat]

Fixing this requires doing #25 first as we need to init the template item at the same time as we load the resource file (instead of the current version where templates are lazy resolved on access)