[ROUTING] Improve app library and port/app manager.

[evanlinjin]

Currently, the way how port/app management works does not support the following:

1. Does not allow applications to listen on multiple ports.
2. Couples the idea of routes & loops.
3. Does not allow multiple instances of the same app.

Further proposals include:

1. Switch from unix pipes to unix sockets.
2. Get rid of the confusing app.Protocol structure.