Move W_DISABLED option to new widget_state_t flags

...and rename to WIDGET_STATE_DISABLED.

  * Widget::state: new field.
  * Widget::set_state: new virtual method.
  * (widget_set_state): new function.
  * (widget_default_set_state_callback): new function.
  * (input_set_options_callback): rename to input_set_state_callback.
  * (widget_set_options): symplify.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Move W_WANT_IDLE option to widget_state_t flags

...and rename to WIDGET_STATE_IDLE.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Remove WDialog::fullscreen field.

(widget_is_fullscreen): new function. Use instead of WDialog::fullscreen.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(dlg_mouse_event): minor refactoring.

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

Initial step: move widget list of dialog into WGroup class.
Inherit WGroup from Widget. Inherit WDialog from WGroup.

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

  * group_set_current_next;
  * group_set_current_prev;
  * group_get_next_of;
  * group_get_prev_of.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
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>
Join widget_state_t and dlg_state_t.

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

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