change react extension from .jsx to react.js

PyCharm flags every .jsx file as having an error because it can’t
resolve the path names to the files that .js version of the .jsx files
that will exist after the assets are compiled.  Changing the extensions
to *.react.js allows PyCharm to detect broken requirejs paths
(dependencies pulled in) and also makes it clearer which files being
included area React components vs. standard JS files.
add jsx directive to react.js files

It wasn’t needed when they were .jsx extension because gulp-react
automatically added it if missing.  Now it needs to be explicit.