apply-to=<window-id> configuration ignores default config behavior after invoked

[aspauldingcode]

After using the feature implemented from #57, I use a command to set the borders style=round or style=square for toggling gaps.
However, after toggling fullscreen on then back off (with another custom script that uses apply-to= for hiding the border), the custom toggle-gaps command only applies to the windows which didn't invoke apply-to=.

Maybe there's a way to reset the border invocation of apply-to=<window-id> like reset=<window-id>, so that it continues to work with regular borders commands that don't use apply-to=<window-id>.

[FelixKratz]

Lets discuss this further in #57