Add possibility to re-parse commit messages in case of regexps change

[okainov]

I'm currently trying to tune regular expressions for my repo and I found out that I cannot reparse commits for the whole repo, only do full import again. It would be nice to have such kind of button which will:

• Go for each commit in the repo
• Apply regexps to find linked issues
• Unlink not-found issues and link new ones

Maybe bullet about unlinking could be optional and available as parameter...

[dregad]

Good idea. Contributions welcome.