Contacts: force left justification on separator headers in contact list.

ported from jellybean branch (http://review.cyanogenmod.org/21573):
original commit:

ported from ics branch.
original commit (http://review.cyanogenmod.com/18903) was not merged.
this fix prevents headers with characters from RTL languages from being hidden
behind the scrollbar.
in most cases headers with RTL characters are completly hidden behind the
scrollbar until the user scrolls down to the next section making the header
to stick to the top (the 'sticky' headers are aligned properly).
to reproduce (in case that you have no contact names in some RTL language):
- switch locale to any RTL language (hebrew, arabic etc..)
- open the people app, the 'ME' contact should be displayed with the
  localized string.
- scroll to the top of the list, the 'ME' header aligns to the right,
  as soon as you start scrolling down the header's text is forced back left
  on the 'sticky' headers.

Change-Id: I3a0b4c45193d43155420fa3effb3f4187bd54953