Support DISPLAYTITLE in article view

Added support for the display title. Limited this to
article view as this seems to be the consistent behavior
across platforms. There was actually a field for this in the
article model, but it was apparently never fully implemented.
Perform nil check when create dictionary in
DownloadSectionsOp.m, and in getHeaderTitle
Section+DisplayHtml.m.

Bug: 63971
Change-Id: I26fe6d723540b67da533e6b916a6a288a4ddc4c9
Prevent app from using css if 200 response but error message found.

Change-Id: I58462c3a20f96df4411f444e049a441c92007aec
Merge "Prevent app from using css if 200 response but error message found."
Fix for occasional crash when clearing saved pages.

Change-Id: I828294b6e0515d4a2d307a833581a5d0ea7de6f9
Work in progress.

Added cocoapods and through it, AFNetworking and HPPLE.

Made Article object use AFNetworking to retrieve sections.

Fixed bug which caused lead sections to sometime jitter
halfway down the page as they downloaded. Was related to
the extra scrolling spacer only being added to the bottom
of the page after all sections had be retrieved. The fix
involved adding the last modified by, other langs, and
the spacer to bottom of lead section so it's always
there, then when non lead sections are retrieved they
are injected just above this footer stuff.

Change-Id: I991fac86a8788d3fd25595849b618a3d1ee7e699