mtr-gtk: migrate from consolehelper to polkit
    
    Previously we used consolehelper in order to authenticate user who wants to run
    mtr-gtk. In Fedora we have newer framework providing access control for
    privileged operations, policykit.
    
    This commit replaces consolehelper configuration and provides policy file for
    policykit and shell wrapper which runs mtr via pkexec. Note that this is not ideal and
    we haven't gained a lot by this.
    
    In the long run we should really decouple gtk frontend and mtr backend. Backend
    then would have CAP_NET_RAW capability encoded in filesystem and as soon as
    possible it would drop that capability and start providing data to be rendered
    by gtk frontend which would run completely unprivileged.
    
    http://fedoraproject.org/wiki/Features/UsermodeMigration
    
    Resolves: #502750