This behavior was intended to help keep the websocket alive, but keeping
the inbox window around can cause some stale frontend state. Also we now
have a keepalive alarm to check for new messages once a minute.
As a chrome packaged app, we have to keep at least one window open in
order to maintain our websocket connection in the background page.
This change replaces the system window frame with custom buttons in the
inbox header, such that the 'close' button merely hides the window
rather than unloading it.
Fixes#237
FREEBIE
