Handle image extensions/filetypes when loading thumbnails

[ots22]

Thumbnails for the models/datasources in the frontend are kept here.

Fix

scivision/frontend/src/App.js

Lines 62 to 80 in 1fe8767

	// Load the thumbnail images
	//
	// require.context returns a webpack object, which is callable.
	// Calling it with the name of a resource returns the path to that
	// resource. It also has a '.keys()' method, which returns all the
	// included resources
	const model_thumbnails_ctxt = require.context(
	'./data/thumbnails/models', false, /\.jpg$/
	);
	// From the webpack object, make a dictionary from the resource name
	// to its path
	//
	// Could strip the leading './' and trailing extension (and then handle
	// several file types)
	const model_thumbnails = model_thumbnails_ctxt.keys().reduce((dict, mod) => {
	dict[mod] = model_thumbnails_ctxt(mod);
	return dict;
	}, {});

to strip the extension and make the lookup work by name (rather than file path - and so support other image formats).