Feature Request: Specify windows that anchors should never show over and/or behind

[vertigo220]

As discussed in #400, it seems ideal to be able to specify what windows/apps/exes anchors should not be allowed to share the same space with. This means not only to not show the anchors over the windows, but to not even show them behind them and to move them elsewhere entirely so they can still be visible (though this could also be individually customized, so when specifying the program the user can choose whether to always hide anchors behind them or always move anchors away from them.