Consider changing the LISTEN_ADDRESS option

[dylanmccall]

As of learningequality/kolibri@351127b, Kolibri 0.16 adds a LISTEN_ADDRESS option. This controls the address Kolibri binds to at startup. It defaults to 0.0.0.0.

For the Endless Key app, it doesn't make sense for the Kolibri server to be reachable from other devices on the network. (In addition, this feature doesn't work on Chrome OS anyway).

Let's try setting LISTEN_ADDRESS to 127.0.0.1. This will also disable the code which broadcasts Kolibri's presence with Zeroconf.

[dbnicholson]

Totally agree. Note that @wjt was messing around with this on Windows in endlessm/endless-key-app#132 but ran into a Kolibri bug with zeroconf initialization. That has presumably been fixed upstream now, but I feel like I tried to set LISTEN_ADDRESS to 127.0.0.1 in my chaquopy experiment and it still fell over. But if we also just remove zeroconf from the equation then it can't be an issue anymore. As mention in #177, I don't see any value in zeroconf as we wouldn't want to broadcast availability of the server in any scenario I can think of.