[ProbesModel] Trivial: Add missing whitespace
[ProbeStore] Optionally ignore broadcast SSIDs.

Add the option for the ProbeStore to ignore broadcast SSIDs. The idea is
to keep two stores, one with broadcast SSIDs and one without. (Switching
the ProbeStore will hopefully be easier than handling it in the model
based on a setting).
[ProbesModel] Provide a store with broadcast SSIDs and a store without to the ProbesModel

This should make it possible for the model to hide/display broadcast
SSID requests as desired.
Add a menu action to hide broadcast SSIDs.

The user can now decide to hide broadcast SSIDs. The current
implementation does not indicate that this has been done, and does not
allow the user to undo this.
Allow the 'hide broadcast SSIDs' option to be toggled on or off

Mark the menu item as checkable so the user can see what option (s)he
selected too.