[Notification] Add API for using buttons and a text input in a notification and getti...

[Notification] Add API for using buttons and a text input in a notification and getting block state

To add buttons tizen.NotificationButton can be used. It allows setting text, an image and an action. An array of buttons can be provided as a value for
"buttons" key in InputInitDict. To use a text input, an object with proper values can be provided as a value for "textInput" key. To get notifications
block state, tizen.notification.getBlockState() function can be used.

[ACR] https://code.sec.samsung.net/jira/browse/TWDAPI-284
[Verification] Features have been tested with an example application which uses new API.

Change-Id: I0d3d2110b3cf37d17e4cf632d18263f493606653