Remove the no_items() method in the networks list table.

If we're missing networks on this screen, we're in some kind of trouble.
Fill out the list table construct() method a bit.

We were complicating things a bit. Now we're being simple and explicit.
Remove unused ajax_user_can method in networks list table
Add documentation throughout the list table class
The network_id should be assumed to be sorted ascending on first view
Use single quotes on output of table row