Instead of adding all screens directly to globalconf.screens, the individual
"scanner functions" now get a screen_array_t as their argument and add the
screens there. Also, they no longer emit the "added" signal themselves (through
screen_add()), but the caller does now does this instead once all screens are
found.
This commit drops the "deduplication" of screens. This likely means that clone
mode causes duplicate screens. This will have to be re-added later.
Signed-off-by: Uli Schlachter <psychon@znc.in>