rules: remove duplicate instance matching for Flash
flash: make Flash with PPAPI work fullscreen (workaround)

In fact, there is nothing to distinguish a Flash window from a regular
window by using only one property. Therefore, we use `name =
"Chromium"` instead. This means that all Chromium windows will be
intrusive. Have to find something better.
dbg: fix `client_info()` function to display provided client

Display the focused client only if we don't have get a client.
flash: correct how fullscreen PPAPI Flash is detected by shifty

`config.apps` can now use a function to do detection.