notifications: rework notification API

 * Note: DBus API compatibility has been dropped

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Fix compiling warning.

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Restore the SQL storage of notifications

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Merge pull request #78 from webOS-ports/tofe/notifications

Tofe/notifications