New API to change format policy on HildonTimeSelector

New API to change format policy on HildonTimeSelector

* src/hildon-time-selector.h:
Added HildonTimeSelectorFormatPolicy
* src/hildon-time-selector.c:
Added PROP_TIME_FORMAT_POLICY
(_check_ampm_format): renamed to check_automatic_ampm_format
(update_format_policy), (update_format_dependant_columns): new functions
(hildon_time_selector_class_init)
(hildon_time_selector_contructor)
(hildon_time_selector_init)
(hildon_time_selector_get_property)
(hildon_time_selector_set_property)
(hildon_time_selector_get_time)
(hildon_time_selector_set_time)
* src/hildon-touch-selector.h: new file
* src/hildon-touch-selector.c
(hildon_touch_selector_emit_changed)
(hildon_touch_selector_block_changed)
(hildon_touch_selector_unblock_changed)
Added functions to allow to block the emission of the "changed" signal
* src/hildon-picker-dialog.c
(hildon_picker_dialog_show): call the parent show before the custom code
* examples/hildon-time-button-example.c
Modified, so now you can configure the time format using the new property

Added a new property "time-format-policy" that allow to choose the time
format: AM/PM, 24H or AUTOMATIC. AUTOMATIC is the default one. In this
case it uses gconf in order to check if the time selector must use
AM/PM or 24H.

Fixes: NB#111606 (HildonTimeSelector should expose API to set/unset am/pm mode)