Initial set up of meta value class

* Moved the meta field form definitions, default values to one file, translations in metabox class as are only used there
* Fix: removed duplicate add_meta_boxes() function and hook
* Framework for autoloading
Rename meta box field definition variable
WP Coding Standards Code Sniffer round & fixing some issues found in general Code Inspection

Code standards based changes (not 100% yet, but getting close):
* Lots of single quotes vs double quotes
* space between ! and condition
* , after last item in array
* variable assignment alignment
* tabs not spaces and other line indentation
* space around parentheses
* try and avoid not using {} with one line statements, only changed when I came across it, there are a lot more instances where this could (should!) be changed as it's very bug sensitive

Other changes:
* Removed some unused variables, added @todo notes about some others
* Properly escape url's:
	- &amp; vs & in url's
	- use of esc_url()
	- use of add_query_arg()
	- use of admin_url()
	- use of urlencode()
* Escaped some &'s in text strings too when it seemed necessary
* Applied esc_js(), esc_attr() in some places
* Fixed a few typo's including a couple which were causing html validation errors

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Bugfixes:
* Explicit variable declaration for js variables and some jQuery efficiency improvements (more needed)
* Admin -> Titles & Meta's -> Post types would show attachments even when attachment redirection to post was enabled
* Fixed: wpseo_invalid_custom_taxonomy() message (html issue)
* Fixed: wpseo_translate_score would never return score, but always the css value

Enhancements:
* Proper field labels for user profile form fields

Other:
* Removed statement for compatibility with WP < 3.4 as minimum requirement for WP SEO is now 3.5
* Removed some old (commented out) code
Fixed "Variable assignment in condition" issues which are prone to bugs

And some more small code style changes
category_rewrite_rules() did not account for get_category_parents() potentially returning a WP_Error object

Fixes: category rewrite rules could have errors for categories without parent categories
DocBlock placeholders for where documentation is missing