* invoices are no longer deleted to prevent double-spends but marked as confirmed.
therefore, during checkInvoice, we also check if the invoice is already confirmed.
* instead of showing FundError (with "fund wallet" and "pay invoice" as options), we now always immediately show an invoice
* since flagging, paying bounties and poll voting used FundError but only allowed spending from balance, they now also support paying per invoice
Co-authored-by: ekzyis <ek@stacker.news>
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