Sync to Ic3303be0c22063abab4684119bd088809838c522

Sync to Ic3303be0c22063abab4684119bd088809838c522

    Add accessibility events & Change 24 -> 32

    Pixmap is created as 32 bits pixels. (RGBA)
    So every client & provider library should access it with 32 bits mode.

    This patch changes 24 bits to 32 bits.

    Add hold_scroll and remove unused string in packet.

    Provider needs to send hold scroll request to viewer.
    In case of scrolling pages from the viewer with mouse_event=true boxes.
    user can confusing with event processing.

    While scrolling the pages, the boxes are able to try to get mouse event from user.
    Then the event and its action can be conflicted.

    To resolve this, the provider should send the scroll hold request to the viewer.
    If viewer get that event, has to freeze the scroller to prevent from event confliction.

Change-Id: I0097f1e67aac5dd3726d753f184a4fc022049a5b