Exit when DBus fails because of insufficent privilges.
Fix monitoring of multiple tasks.

For some reason the method that was called in a separate process to
monitor a task monitored ALL tasks, so with multiple tasks we got
multiple checks that are unnecessary, nasty race conditions and so on.
Move the backup folder logic into own module.
Fix install script.

The working directory is now set correctly.
Make the logging format accessible through constants.

Before, they were hardcoded.
Fix main executable.
Update dependencies in setup.py.
Update tests.
Simplify sleep algorithm.
Add methods to share data with other backup folders.
Fix construction of the rsync logfile path.
Tidy up core modules.
Add first draft of a man page.
Update documentation.

Sphinx can not be used to automatically generate documentation for all
modules.

Some docstrings were written from scrath, others were converted, as the
old ones had invalid syntax and formatting.

./make-html-docs.sh can be used to automatically generate html pages
containing documentation and display them in the default browser.^
Fix validation of configuration file.

Every key not found but needed default to None now, so we can filter
them out and fall back to default values. Additionally, when validation
fails the error message lists every single error.
Merge branch 'overhaul' into develop