* (bug) treat xmr wallet directory as required
The wallet directory configuration setting is required
because the `UIMoneroLikeStoreController`'s
`GetMoneroLikePaymentMethodViewModel` method checks if the wallet file
exists, and to do that in needs the directory.
* (feat) xmr settlement thresholds
Adds the ability to select zero, 1, 10, or a custom number of
confirmations as the payment settlement threshold.
* (review) fix validation message not showing
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Co-authored-by: Henry Hollingworth <henry.hollingworth@alcoa.com>