elementary/focus : Add four more focus direftions. ELM_FOCUS_UP, ELM_FOCUS_DOWN,...

elementary/focus : Add four more focus direftions. ELM_FOCUS_UP, ELM_FOCUS_DOWN, ELM_FOCUS_RIGHT, and ELM_FOCUS_LEFT. These are for supporting elm_object_focus_next with four directions. And I added elm_object_focus_next_object_set(get). By setting focus next object manually, developer can set its own first candidate of focus next. Lastly I added elm_object_focused_object_get, for easy finding of current focused object in one object sub-tree.