Fix a couple of bugs in folderselectionmodel.

 -Signals would not get emitted correctly when re-including an excluded path.
 -Hidden folders never showed up as IncludeIherited.
 -Partially checked status would get set incorrectly for paths with similar
names, i.e. under the same parent folder and one starts with the name of the other.

The rest is just clean-ups.
Add "advanced" config page and option to show hidden files.
Add a couple of hidden folders in home directory as default excludes.
Update TODO file
Add compression level as an advanced configuration option.
Cosmetic changes to BupJob.