Updated secure download and file generation methods

Information: we have updated the format for generating files for downloading (.txt file name).

Now the algorithm is 10 times more complicated and it is impossible to select a download link because added many checks.

Moreover, we have significantly improved the work with payment gateways (several new types of payment have been added - for example, through the Fast Payment Service), which is very convenient and fast. No need to enter card number, CVV/CVC code and other information.

We fixed a number of errors and conducted testing for SQL injection throughout the site to eliminate the possibility of downloading files by other users.