convert inter issue links

Currently, links between issues within the description or comments aren't converted but treated as ordinary text. For example: 'PROJA-123' or 'ANOTHERPR-678' are highlighted and linked with the corresponding issue in Jira whereas in Redmine, they are just displayed as plain text.

There probably should be some kind of post processing job that uses storage.db to convert these issue identifiers to Redmine issue links.