WGroup API: move add/delete widgets API from dialog to group.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(wid_t): new type for widget ID.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
WGroup API: group_send_broadcast_msg.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
WGroup API: init/deinit group.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Reimplement find widget functions to support groups.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(widget_is_active): reimplement to support groups

...and related changes.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
W_TOP_SELECT: new widget option to place widget on top of other widgets in group.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Start reimplementation of widget selection.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>