Tor writes to a temporary file and then renames it over the old
file, if any, so CLOSE_WRITE never occurs. The old code was
working in most cases because it received IGNORED when the old
file was unlinked and didn't check the event type.

* Move PluginConfig out of bramble-android. Projects using bramble now need to provide it.
* Add a PluginConfig#shouldPoll() method which can be used to disable polling altogether.
* Move Poller instantiation to the PluginManager.

This ensures we bind to the wifi interface even if it doesn't have internet access and there's another interface with internet access (e.g. mobile data).