PDB files downloading should use RESTful API

Currently, the link to download PDB files is stored in the "data/DBXRefRegistry.txt" file. The second column in the entry is a link to open in the browser, if UGENE can't download and visualize it. The third column is a link to download the file.
These links should be updated: I have not found our links in the RCSB PDB documentation. Otherwise, there is a RESTful API to work with the database.

There is an issue related to deprecated links: some IDs become case sensitive. E.g. '1fdl' can be downloaded by UGENE, but '1FDL' cannot.