enable private logging on f-droid webservers

Having the download counts as one source for the "popularity contest" system fdroidclient#396 (closed) will make it provide much better data than just the user submitted data alone. Tor Project has a proven method of logging web hits without tracking too much information. I just wrote it up:

https://guardianproject.info/2017/06/08/tracking-usage-without-tracking-people/

Since all the f-droid.org servers run Apache, it will be easy to do. First, enable mod_geoip:

# apt-get install libapache2-mod-geoip
# a2enmod geoip

2 then in the site config file, change the logging config to:

LogFormat "0.0.0.0 - %u %{[%d/%b/%Y:00:00:00 %z]}t \"%r\" %>s %b \"%{Referer}i\" \"-\" %{GEOIP_COUNTRY_CODE}e" privacy+geo
CustomLog ${APACHE_LOG_DIR}/access.log privacy+geo

Then once we have that data source, I'll rework the stats scraper to store those logs in private gitlab repos. Those will then be used as raw data for rating apps based on popularity, in combination with a bunch of other things.