Notify user when libbitcoin server is down

[cpacia]

I updated the check_for_payment api call to return

{"success": False, "reason": "libbitcoin server offline"}

when the libbitcoin server is down. We should probably put an error message in that top part of the order model telling them that the server is down, their coins aren't lost and the transaction will show when the server comes back online. Also point them to the settings if they want to change their libbitcoin server.

[jjeffryes]

Recommended solution: inside js-buyWizardHero add a new section that is initially hidden with the hide class. When the offline message is received, show the hidden section with the offline message and a button with a link to #settings/advanced.

[drwasho]

Nice work @cpacia

[drwasho]

This is quite important as users will be confused as to why their transactions aren't being processed.

[drwasho]

Updated @jjeffryes ?

[jjeffryes]

@drwasho this hasn't been added yet

[drwasho]

Done and dusted.