Make it work on rooted pre-Lollipop devices

[benhylau]

• Cleaned up and Rx-ified classes that manage cjdroute and config generation
• Pre-populate cjdroute.conf with public peer
• Works (start/stop of cjdroute, ping and browsing) only on rooted pre-Lollipop devices

[benhylau]

Some more notes:

1. Switched everything to Rx to better manage the threads, unsubscribe when the views are gone, etc.
2. The default route we discussed gets removed automatically by the system once cjdroute shuts down. Not too intrusive.
3. Cleaned up the README and made tasks in issue tracker for the old TODOs that aren't already in there. https://github.com/benhylau/cjdns-android/blob/run-as-su/README.md
4. Persist PID over Java process restart that @lgierth and I talked about. This works fine most of the time. It isn't perfect, because if the kill somehow failed, we still remove the PID from data store. We can improve this later by checking for any cjdroute process.

@sssemil @lgierth @kpcyrd @prurigro Will merge after I get a few approvals.

[sssemil]

Sounds ok, but can't test it, so I'm neutral about this one.

[benhylau]

Works on my Nexus S running 4.4.4. Seems to have problems on a Gingerbread device, but merging for now.