Fix a way how users and URLs are treated in report
Fix a way how users and URLs are treated in report

In case of user replacement there was a bunch of regular expressions
used, which was an overkill. Substituted them with one generic regexp.

Moved method which is responsible for substitution to the base class.

Last change is a cosmetic one - uploaded files are represented as
absolute path with file:// prefix, so that it is easier to open it with
xdg-open for example.

gryf/slack-backup