A few small changes to the phpBB3 importer (#4321)

* Reconnect to phpBB3 database on connection loss

* Map geek smiley to :nerd: emoji in phpBB3 importer

* Import PMs to yourself from phpBB3

* Allow empty table prefix in phpBB3 importer

script/import_scripts/phpbb3/support/smiley_processor.rb

@@ -47,7 +47,8 @@ module ImportScripts::PhpBB3
         [':?:'] => ':question:',
         [':idea:'] => ':bulb:',
         [':arrow:'] => ':arrow_right:',
-        [':|', ':-|'] => ':neutral_face:'
+        [':|', ':-|'] => ':neutral_face:',
+        [':geek:'] => ':nerd:'
       }.each do |smilies, emoji|
         smilies.each { |smiley| @smiley_map[smiley] = emoji }
       end