Empty $integrations array prevents defining $links

Empty $integrations array prevents defining $links which causes a notice for undefined var and warning in `implode()`
Issue #2245 / Disable Integrations Tab if empty
Merge pull request #2252 from kloon/master

Show selected attributes based on id and not slug in product edit pages.
Merge pull request #2246 from entr/patch-2

Issue #2245 / Disable Integrations Tab if empty
Prefer empty function over ! count for this #2246
Merge pull request #2244 from entr/patch-1

Empty $integrations array prevents defining $links
Use meta to prevent double tracking Closes #2248
Clean up variation display in admin. Closes #2241.
Fix fatal error, `empty()` only supports variables (prior to PHP 5.5)
Merge pull request #2255 from GeertDD/fatal_empty

Fix fatal error, `empty()` only supports variables (prior to PHP 5.5)
sort icon
Support desc_tip in settings api Closes #2251.
orders icons / action buttons
Order status icons

completed = check
pending = dash
cancelled = cross
failed = altert
on-hold = clock
refunded = arrows
processing = dots
prevent undefined state placeholder
S Korea has no states. Closes #2257.
Fix checkout field visibility after switching country
dont trigger tab actions for shipping/billing
cleanup save function
When editing checkout fields, only refresh totals if required address fields are filled.