feat!: type script usability and better request return values

BREAKING CHANGE: the IContentStorage and ILibraryStorage interfaces were extended with the `getFileStats` method, which returns size and creation time information about files. The file system storage classes and Mongo/S3 storage class were extended to remain compatible.

Furthermore, there was a lot of refactoring to improve typing and extensibility.

package.json

@@ -2,6 +2,7 @@
     "name": "h5p-nodejs-library",
     "version": "2.0.0",
     "description": "The H5P-Nodejs-library is a port of the H5P-Editor-PHP-library and the H5P-PHP-Library for Nodejs.",
+    "license": "GPL-3.0-or-later",
     "repository": {
         "type": "git",
         "url": "https://github.com/Lumieducation/H5P-Nodejs-library"