elm_datetime: Parses the format recursively.

elm_datetime: Parses the format recursively.

Summary:
Some of locale formats convert as extension format.
For example,
             uk_UA d_t_fmt is "%a, %d-%b-%Y %X %z".
             The %X will convert as %T.
             The %T format has to convert one more time to convert as %H:%M:%S.

ref : https://lh.2xlibre.net/locale/uk_UA/

We need to parse the format recursively to support that kind of case.

@fix

Test Plan:
Change the locale as uk_UA.
Run elementary_test -> datetime
See the time field is not appear.

Reviewers: jpeg, cedric

Subscribers: cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D5021

Change-Id: Ie088a4558d3688542e9bcf43dacd1a9a339b433e