Need to update jQuery from 1.9.1 to >= 3.5.1 in order to fit data security

[PM84]

To meet the requirements for data security, we need an update of the jQuery libraries to the current state of the H5P developers (3.5.1) needed. For this I have created a pull request for you. #127

[sr258]

We couldn't wait for the update, so we've prepared an unofficial release that patches to jQuery 3.6.0 (and also uses a newer H5P core): https://github.com/mebis-lp/h5p-wordpress-plugin/releases/tag/1.15.3.1