Add missing "leichte Sprache" classification and English alternatives

English pages are not yet harvested. Based on an analysis of the website, the best way forward is to chekc on the already harvested German pages whether a link to an Enlish version is available and, if so, to add this as an alternative to the dataset. In addition, this MR also adds four pages in Easy German as well as merges the manual dataset into the UVK origin entry.