BugID: 13714 - Modify local navigation parsing

This maintenance script goes through MediaWiki:Wiki-navigation
message on given wiki, replacing
'blogs-recent-url-text',
'blogs-recent-url',
'portal-url',
'forum-url'
with their respective translations.
Removing unnecessary purge, variable, change way of creating the user.
Code review changes;

We want to replace messages in all cases except
when there is a Nav Article with only one revision
edited by user Default - which means it is an
import from starter Wiki
Adding wfWaitForSlaves() just in case
Merge pull request #341 from Wikia/consumer-QB-1-bugid-13714

Maintenance script for Bugid 13714