Pause channel

[manumoreira]

In several situations we need to stop using the channel
- Run out of credit
- Got an issue in the channel configuration
We want to offer an option to pause the channel to hault the enqueueing of respondents into the channel
It is critical to make sure this will not harm the survey in any way... only adding delay to the contact window

[manumoreira]

We should explore the possibilities of reusing the existing code for this.
Currently when a channel disconnects or fails it informs the survey and it stops sending contact attempts. It also send emails to the admins.
This was implemented in #1449

[manumoreira]

We came to these options in our last sync:
The pause action should be done inside each channel in surveda

We can use the FAB that's already used in many other screens
Once the channel is pause the user will be able to see the status in the channel list