Added time-error signal - NB#22155

Added time-error signal - NB#22155

* hildon-widgets/hildon-time-editor.c:
        (hildon_time_editor_class_init): added time-error signal
        (validated_conversion): added 'error_code' output parameter.
        (hildon_time_editor_real_validate): use 'error_code' and trigger
        'time-error' signal when apprpriate.
        (highlight_callback): avoid revalidation

        * hildon-widgets/hildon-time-editor.h (HildonTimeEditorErrorType):
        new enumerative type for error types
        (_HildonTimeEditorClass): added time_error signal

        * hildon-widgets/Makefile.am (hildon-libs-enum-types.c): added time-editor.h