Read issue url from configuration.

Instances which are build from a forked code base can now point to their
issue system. The default is pointing to the original innoQ statuses
GitHub repository.

Relates to #137.
Add link to commit hash on info page.

The configuration parameter should point to the repository's state of
the given Git SHA hash. This allows easy browsing of the code base used
by the running instance.
By default the parameters points to the GitHub tree of the original
innoQ statuses repository.

Fixes #137.