temporary fix - add Ewk_Context to ewk_notification_showed to make WRT compile

temporary fix - add Ewk_Context to ewk_notification_showed to make WRT compile

Context was not used and we removed it, but WRT assumes that
ewk_notification_showed takes context as one of the parameters
and after our Notification API refactoring it doesn't compile.
WRT will update to the new API, but for now we need this temporary
fix for it to work.
Reviewed by: Piotr Tworek, joonhwan kwon

Change-Id: I6d1fad4c07c4bdfdbef3511864a4b71abb71b429
Signed-off-by: Tomasz Czekala <t.czekala@partner.samsung.com>