More easily support Select2.full.js

[cooperka]

Helps with use-cases like those described in https://github.com/rkit/react-select2-wrapper/issues/8 and https://github.com/rkit/react-select2-wrapper/issues/71. Fully backwards-compatible.

Users who wish to include the full version should change their import as follows:

-import Select2 from "react-select2-wrapper";
+import Select2 from "react-select2-wrapper/lib/components/Select2.full";

See individual commits to verify the base code is unchanged.