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.
mutlselect case #2259
More descriptive variable name
Don't convert zero values to empty string

PHP's empty() function returns true for 0, 0.00, "0.00" and other 0 variants.
That means woocommerce_process_shop_order_meta() will convert item meta with
a 0.00 or similar value to an empty string, which can break things that expect
a float or number. This commit fixes that.
Merge pull request #2262 from thenbrent/shop_order_meta

Don't convert zero values to empty string in woocommerce_process_shop_order_meta()
rejig the hooks Closes #2263.
Closes #2261.
Fix multiselect name Closes #2259
Fix saving as array #2259