Mountpaths indicate mount points of external devices. Files
located under such paths should not be removed on sync, because
they may have not been deleted, but are just inaccessible right now.
We now resolve symlinks when adding, so we can properly check
whether a path is excluded or not. This accidently also
helps with duplicates.
Excluded paths are hardcoded and can also be appended to
by the user using the settings.
Closes: #34
