Tracker: add option to add file to blocklist

[nephele]

In the Add-ons section for files there should be an optin to "Add file to blocklist"

This should be available for files that are present on a packagefs mount, using this option should add the respective file to the packages file with a blocklist entry and remount the package (or tell packagefs in another way to change this view)

edit: another neat thing might be to have a "shadow" of the files visible only in tracker (that is perhaps no real inode entry presented in the posix api, but exposed to tracker with a specific call) And then have an option to unhide them