clearing applications list

[kay van der Zander]

because the list needs to contain everything you want to restrict, clearing it to start over or lift of the parental control is taking a long time. add a clear button or reverse it to add the allowed apps only in the list. (this is always less if you also take binaries in account. this could also reduce the daemon cpu time. checking the allowed list is always smaller and less cpu time then checking a blocking list).