Created separate network package, moved KerplappHTTPD there.

Moved the HTTPD subclass we use to the new network package. Updated
references to KerplappHTTPD as required. With coming Network Service
Discovery support there will be more network related classes. The parent
folder is looking a little cluttered lately.
Adding rudimentary Network Service Discovery.

Service advertisement is wired up to the HTTPD instance & wifi status.
Presently using the built-in Android support for NSD added since API
level 16 (Jelly-Bean). This will need to be addressed if we want to keep
the Kerplapp target-api at a reasonable level. Likely we will have to
translate the NsdHelper to use jmDNS or another external lib we can
ship.
Merge remote-tracking branch 'origin' into mdns
Moved service reg/dereg, minimized NsdHelper to just service reg.
Adding preferences for network service discovery & repo name.

Now allowing network service discovery to be disabled (enabled by default). You
can also set a repo name which will be used for network service advertisement as
well as in the repo index.xml.
Use an FDroid specific NSD service type, based on SSL preference.

NSD service types follow a convention _protocol._transport. Previously
Kerplapp was advertising an _http._tcp service generically. It makes
more sense to advertise a _fdroid._tcp service so the FDroid client can
run a discovery that it knows won't return generic non-FDroid repo HTTP
servers.

Further, we should advertise _fdroid._tcp when the use_ssl preference is
disabled and _fdroids._tcp when it is enabled to indicate to the
discovering peer whether we are advertising an HTTP or an HTTPS FDroid
repo.
Merge branch 'master' into mdns