add xfixes extension
add selection(clipboard) handling

2 hooks added, selection_notify and selection_change
add clipboard widget, display text in the selection(clipboard/primary)
remove timeout_id after remove the timeout on clipboard widget
add support to blacklist clipboard windows by wm_class

not all clipboard windows have wm_class(or other useful props),
the one i need does(keepassx)
Merge remote-tracking branch 'Roger/clipboard_stuff' into develop
Allow no chopping of clipboard text