Compress location lookup using gzip.

This commit introduces optional compression of the location lookups. Some code cleanup for elements shared between lookup and uploading.

Closes #446.

Todo: move most of the communication code into NetworkUtils.
Add number of GPS satellites to the main screen.
Block Adelaide Metro Public WiFi.

First reported by @micolous. Closes #458.
Decided to use BSSID instead of SSID due to a relatively common name in the SSID field (```PublicWiFi```).
Merge pull request #459 from tamcap/gzip_location

Compress location lookup using gzip (@tamcap)
Merge pull request #462 from tamcap/Adelaide_BSSID

Block Adelaide Metro Public WiFi (@tamcap)
Merge pull request #460 from tamcap/gps_display

Show number of GPS satellites used / visible on main screen (@tamcap)