Also `s/coinJoinEnabledChanged/showCoinJoinChanged/g` to establish a
naming convention that will be used soon.

This should fix the misalignment of the `subFeeFromAmount` `QCheckBox`
compared to the rest of the `QCheckBox`es

Review with `git log -p -n1 --ignore-space-change --color-moved=dimmed_zebra`.

Review with `git log -p -n1 --color-moved=dimmed_zebra`.

Review with `git log -p -n1 --color-moved=dimmed_zebra`.

Inheriting the whole structure is overkill just to use `tr` and `hash()`
is used in hot loops so we should cache the value in the ctor.

Also remove dead variable.