Fix php notices from missing 'feed' and 'owner' attributes.

Default and suggested channels are stored in a json-formatted string in a column of the `settings` table (which has only one row).  Sure.

These get decoded into `stdObject` instances, which are then used in a couple of loops (on both the admin side and the public side) to render the channels.  The problem I ran into is that the objects stored in the json string only have the attributes defined that they have values for, so I was seeing a lot of php notices when accessing `$channel->feed` or `$channel->owner` for channels that didn't have those properties (actually, all channels should have `feed` defined, but that is a separate issue #89).  On production I'm sure these notices don't render, and there isn't any real harm.  Locally, they can cause some problems (like the notice text accidentally getting saved as the value for `feed` or `owner`). Most of all, they should just not be happening.  

:eyeglasses: @Deimos