These improvements on the server app handler should help writing
and running stand-alone apps.
The two main goals are:
1) "simple" configurations should work automatically; the parameters for
the app are derived from the Listen and BaseURL of the Camlistore
server.
2) More advanced configurations, such as being behind a proxy, should be
easily configurable through the app's Listen, BackendURL, and ApiHost
parameters.
I had worked on them while doing the scanning cabinet app, and I am
backporting them now since we haven't landed the scanning cabinet yet,
and people have been having trouble setting up the publisher.
pkg/app/app_test.go is gone because app.ListenAddress is now dumb. The
hard work is done in pkg/server/app instead.
Fixes#818
Change-Id: Ice2610d6bac611b209cc3a928e67fa6093a41d3e
mpl