Updating the 'class-metabox.php'

I needed to add a variable on this filter to allow the developer to know what post is been requested, instead of just the post content.
Merge pull request #239 from tudoparawp/master

Updating the 'class-metabox.php'
Add option to disable slug stop word cleaning
Add $post to all instances of `wpseo_pre_analysis_post_content` filter
Move help on Titles & Metas admin page to help tab
Updated translations

Updated de_DE, fa_IR, fi, hu_HU, it_IT, pl_PL, sv_SE and tr_TK