Small fixes for alt sub editor integration

Small fixes for alt sub editor integration

This commit applies some polish to the alt sub editor integration:

 - Prevent spinner from displaying continuously when adding a
   subscription
 - Hide the editor when changing subscriptions to limit confusion
   about what is loaded
 - Dynamically add a node to the tree view when adding a subscription
 - Make sure the 'View/Edit' tab gets populated when backing out of
   the stream or item view
 - Apply some default link styles

Signed-off-by: Dan Wells <dbw2@calvin.edu>