Normalize upload file name (#606)

* Generate secure token using crypto rand

* Normalize names of uploaded files

* revert token.go accidentally added to commit

* better input filename normalization using transfrom chain

* remove unused line

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Co-authored-by: Alexey Kostin <a.kostin@corp.mail.ru>
Co-authored-by: Andrea Spacca <andrea.spacca@gmail.com>