Added new "byemail" action to the new users log

Added new "byemail" action to the new users log

This allows to display the "password sent by e-mail." string in the user's language
since it's now in the action text rather than always in content language due to the
fact it was hardcoded in the log's comment.

Insertion of log entries for the new users log is now acomplished using the
ManualLogEntry class rather than the old LogPage one.

Removed 'newuserlog-byemail' message since it's no longer used (also checked
extensions in Wikimedia's Git repo).

IRC notifications will use the same message for 'create2' and 'byemail' for backward
compatibility. The only difference is that 'byemail' entries will no longer have
"password sent by email." in the comment.

Change-Id: Icdf1d714259d054cf8c256faf894c533be0dc73c