Add optional TCP support

[jleung51]

This is related to the issue from pm-android about reducing the amount of data used.

[landalex]

Do you mean WebSocket support? Or a long-living TCP connection? The current HTTP API is already using TCP, but making a new connection each request (which probably doesn't have ridiculous overhead since it's once every few seconds, but might be worth getting rid of).

[jleung51]

Ah, seems like I don't understand the solutions well enough then. Are either websockets or a long-living TCP connection more viable?

[landalex]

I think WebSockets are a better choice for the job, because they work at a higher level (and we don't really care about the details of the connection, just that it's efficient).