Verification of all uses of meta-robots-adv

* Added validation routine
* Added 'site-wide default' option to meta box choices
* Changed default for meta value from 'none' to '-' (=site-wide default)
* Refactored creation of the robots headers tag to take this into account:
	- prio 1: post specific settings (either multivalues or none)
	- prio 2: site-wide settings
* Adjusted the height calculation in the meta box field to the WP3.8 admin theme (might give whitespace in older WP versions, but rather that than a scrollbar in newer versions)

@todo:
Add upgrade routine to
1) validate all 'old' values which may be garbage
2) change default from 'none' to '-'

@todo
Verify headspace meta-robots-adv input values alignment with our values for import routine

Also:
* Fixated meta checkboxes to only have 'on' or 'off' as valid values
* Made the Google+ and Facebook post descriptions translatable by WPML
Verification of all uses of meta-robots-noindex and meta-robots-nofollow

* Added validation routine
* synchronized two different instance of Robots Meta import routine - one should probably be removed

@todo:
Add upgrade routine to validate all 'old' values which may be garbage

@todo
Verify WooSEO meta-robots input values alignment with our values for import routine
Verification of all uses of snippetpreview, focuskw, metakeywords, bctitle, sitemap-include, sitemap-prio, sitemap-html-include, canonical, opengraph-description, opengraph-image, google-plus-description

Also:
* Added validation routines for two types of urls
* Added line break removal for textarea fields
* Fixed a potential "$term is not an object" bug in frontend metakeywords() method
* Moved check for robots site-wide option from do_meta_box() to get_meta_field_defs() method
* added {} to various conditionals without {}

@todo:
* Verify where google-plus-description is being used, can only find the input, not the output
Verification of all uses of title, metadesc, redirect and linkdex

Also:
- enabled new get_value() method, returns empty string if no value found
- added validation for linkdex value
- refactored save_postdata() method
- typo fix
- renamed some parameters for auto-documentation purposes
- Fixed: wpseo_translate_score() calls were passing unintended wrong parameters like so:
`wpseo_translate_score( round( $perc_score / 10 ), $css = false );`
as the assignment worked, `$css = false` translates to true....
Fixed by changing to:
`wpseo_translate_score( round( $perc_score / 10 ), false )`
Form prefix variable to js & usage
Replaced all used of wpseo_get_value() with WPSEO_Meta/self::get_value()
Small tweaks & commented out addition of meta keys to uninstall routine