Add age and gender options to intro sequence

As per [1], this patch adds support for gender and age attributes to
the user's profile. This patch is restricted to modifications to the
intro screens (gender and age selection are included after the user
selects a color).  The AboutMe section of the Control Panel, which
includes mechanisms for adjusting gender and age will be in a
follow-on patch. The artwork used on these screens is added by [2].

Note: This feature as discussed and approved by the design team [3].

The birth time is stored in GConf:

'/desktop/sugar/user/age'
'/desktop/sugar/user/birth_timestamp'

and in gsetting:
'/desktop/sugar/user/birth-timestamp'

The gender is stored in GConf and gsettings:

'/desktop/sugar/user/gender'

[1] http://wiki.sugarlabs.org/go/Features/About_Me
[2] sugarlabs/sugar-artwork#23
[3] http://meeting.sugarlabs.org/sugar-meeting/meetings/2014-01-07T22:18:04