[Bug]: When paying LN invoice that has no 'description' the value 'Bitkit' is used

[ovitrif]

If the receiver hasn't included a 'description' in their LN invoice then we send with value 'Bitkit' by default which cannot be overridden. We call this 'note' in the app. This is not a good idea because the receiver is not expecting a value and an unexpected value can be misleading (e.g. for accounting purposes). We only do this with the iOS app and not Android afaict.

[jvsena42]

Fixed by #725