jQuery tabs code not checking

So the tabs code is always running even when the wpseo metabox isn't
shown. This just checks to see if the tabs screen is displayed before
checking the hash or default. If other metabox use tabs this won't mess
with them.
Fixes hash error after being redirected from FB API + some code improvements to wp-seo-admin.js
Use jQuery instead of $
#521 If the publish date of the post is later than the modified, make that the "last_modified" in the sitemap for googles eyes.
Fixed changelog bug and added contributor
Removed screen_icon() calls
Readme update
Fix double robots header, WP native settings will (and should) be respected
readme
Overwrite global singular robot values on singular items with singular specific robot items

Fixes #562
resolved readme conflict
Merge pull request #522 from mindingdata/master

Fixes issue #521 (Last Modified In Sitemap), props @mindingdata
Update readme for last merge
Merge pull request #506 from dannyvankooten/master

Check if tab hash is correct after being redirected from Facebook API, fixes #505. Props @dannyvankooten
Update changelog for last merge.
Fix as suggested [here](https://github.com/Yoast/wordpress-seo/pull/513) by @raugfer for 404 when pagination base has been changed.
Closes #513
Merge pull request #352 from imageinabox/master

jQuery tabs code only working when it's actually WPSEO's tab in a metabox. Props @imageinabox.
Update readme for last merge.
Merge branch 'master' of https://github.com/Yoast/wordpress-seo
Merge remote-tracking branch 'jdevalk/master' into error-object-as-term

Conflicts:
	readme.txt