Handle invalid customer id

An invalid customer id is an error from braintree, so handle the error and
return an empty list of payment methods.

Refactor command list to use composition

Also rename buy credit to top up

Add btc_addresses to Customer

And use that in registration instead of implementing it inline

Command to get to the credit card settings page

Add plans and electrum structure to example

Reply to extdisco with sip server

fix config sample syntax

Spec says we must reply to all IQs

So say feature-not-implemented if we haven't got it with some other handler.

Merge identical cases

Validate that amount of credit to buy is in valid range

Rename buy-credit to buy credit

When no plan, all plan attributes are nil

Merge branch 'conditionally-show-commands'

* conditionally-show-commands:
  Only show buy credit option if customer has a plan and a credit card
  Show commands conditionally (plus add voicemail record command)

Only show buy credit option if customer has a plan and a credit card

Show commands conditionally (plus add voicemail record command)

Refactor to a factory that allows commands to be shown conditionally, so that
the voicemail record command can only be shown if the customer has a forwarding
target set up.

Merge branch 'credit-card-bonus'

* credit-card-bonus:
  Insert bonus when paying by credit card

Merge branch 'tel-search-temp'

* tel-search-temp:
  No tel picker yet, so just go to the webpage

Use before filter to actually come before everything

Otherwise we go in hierarchy order and stanza comes last.

Merge branch 'passthrough-commands'

* passthrough-commands:
  Pass through commands we know the SGX can handle
  Pass everything from SGX to user, not just <message/>
  Remove some of the noise from the command list

Insert bonus when paying by credit card