Migrate to GEO IP 2 (Related #1471) (#1529)

* Migrate to GEO IP 2, because support will drop in April

* Change all links of maxmind to https
* Update maxmind database dependency and add javatar to extract
the database from the tar archive
(now only a small difference in jar file size -> ~80KB smaller)
* Verify downloaded archive using MD5 (There are no other checksums available)
* Migrate to Java NIO instead of old java file I/O (Feedback?)
* Internal Optional usage for nullable values (Feedback?)

Minor:
* Schedule a Bukkit async task instead of creating a thread manually
* Validate ip input string
* Extract validation into single method
* Close all resources safely using try-resources

* More https links

* Add documentation

* Set the same last modification as in the tar archive

* Fix tests

* Comment how the legacy API responded to unknown entries

* Document missing function param

* Document our maxmind dependency modifications

* Include time unit into constant

* More logging for downloading the database

* Add missing return if the database cannot be found

* Delete temporarily file after working with it

src/main/java/fr/xephi/authme/settings/properties/ProtectionSettings.java

@@ -22,7 +22,7 @@ public final class ProtectionSettings implements SettingsHolder {
 
     @Comment({
         "Countries allowed to join the server and register. For country codes, see",
-        "http://dev.maxmind.com/geoip/legacy/codes/iso3166/",
+        "https://dev.maxmind.com/geoip/legacy/codes/iso3166/",
         "PLEASE USE QUOTES!"})
     public static final Property<List<String>> COUNTRIES_WHITELIST =
         newListProperty("Protection.countries", "US", "GB");