ebay item specifics - save/update specifics fix

Bugfix
If we need to save empty item specifics (or overwrite existing with empty an line if user decided to remove everything),
"SET-EBAY?itemspecifics=" doesn't work. At least we need to pass something there, like carriage return -
"SET-EBAY?itemspecifics="+encodeURIComponent("\n")
See, if we had pure json calls, we could easily pass "ebay:itemspecifics":"" to reset the field (like in adminUIProductPanelExecute)
But in adminProductUpdate call we have json + uri encoded commands/params.