Trigger toast messages in cynara PrivacyPlugin, once per session

Trigger toast messages in cynara PrivacyPlugin, once per session

Toast messages will be generated from server side cynara plugin. The answer
is then cached on client as long as the session parameter of cynara check
is unchanged. When client performs a check with changes session argument,
the cached value will be discarded, client will send check request to cynara
service again, triggering another pop-up.

Change-Id: I28d2eb43bdbf54362c9088dfb1405016a4bd271a
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>