Add dialogue action for sending over a different channel

[justinvdm]

We need a way to choose to send a single message over a different channel (for example, SMS) than the main channel the dialogue conversation is being run over (for example, USSD).

[justinvdm]

@SteveBarnett Ready for review.

The content in the template probably needs changing, would like your input there.

Also still need to put a 'You need to hook up this channel on the routing screen' message somewhere. Only showing the message when it hasn't been hooked up is a bit more complicated, so we either need to come up with a message that makes sense either way, or add a context-dependant message in a separate PR.

[hodgestar]

Looks good to me. I think the Travis build failure is spurious (it only happened on Python 2.6 and it was a timeout during the PhantomJS tests) so I restarted the build.

[justinvdm]

@hodgestar thanks for review :) I'm going to wait for @SteveBarnett to take a look at the content, html and css parts, because I'm pretty sure some improvement will be needed there.

[SteveBarnett]

@justinvdm: content in the template looks good to me. It's consistent voice and tone with the other bits. I think #1046 will do the most to make this bit less confusing. I will add the need to hook up msg.

[SteveBarnett]

@justinvdm I was thinking about adding "You can set this in Configure channels," but was worried about people clicking that and either losing work (from not saving) or getting lost (if we had used target="_blank" on the link).

[justinvdm]

@SteveBarnett thanks for the change :) ya, also thought about that, I think its okay as is though.