Channel closing: improve warning/error message to clarify automatic fee adjustment

[myxmaster]

Describe your enhancement idea

When you try to close a channel with a too low fee, LND answers e.g.:

unable to process close msg: latest fee proposal excees max fee: 0.00000468 BTC > 0.00000453 BTC

The nodes auto negotiate a fee, so the channel close is still happening, but Zeus gives the impression that it is an error and the close could not be processed. Most users will probably try to increase fee and click button "CONFIRM CHANNEL CLOSE" again.