lonelypages.py: ported to core

Ported lonelypages.py to pywikibot core. Removed some unnecessary inline
comments from the code. Also shifted messages to i18n TranslateWiki (see
I9b3506d1e801909a2b1d25f6d82063cdca195d26).

Change-Id: Ic832222ec22c90842388ab78c2220af15a567802