cpp: IFD: Rename libtiff field wrapping methods to getRawField and setRawField

This avoids confusion with the getField<> method which returns a Field<>
object, and prevents any percieved ambiguity with overloading since while
it works, any errors can be confusing since it's not necessarily clear
which method is being called.
cpp: IFD: Allow getting of a const Field object

This allows read-only Field access within const contexts, e.g.
from a const IFD reference or in a const IFD method.
cpp: tiff: Add Sentry error fallback

Allow provision of useful messages for the cases where libtiff
doesn't provide a useful error message.
cpp: IFD: Add getters and setters for PixelType

These are convienience functions which map SampleFormat and
BitsPerSample to and from the PixelType enum.
cpp: IFD: Add skeleton implementation for image reading and writing
AIM: fix offset calculation for > 4GB files
cpp: tiff: Storage ordering is based on TIFF PlanarConfig
PCORAW: fix offsets for files larger than 4 GB
cmake: Add missing include directories

For platforms which do not have the headers on the standard
search path.
Merge pull request #1347 from melissalinkert/aim-offsets

AIM: fix offset calculation for > 4GB files
Merge pull request #1348 from melissalinkert/pcoraw-4gb

PCORAW: fix offsets for files larger than 4 GB
Merge pull request #1349 from rleigh-dundee/cmake-includes

cmake: Add missing include directories
Merge pull request #1343 from rleigh-dundee/cpp-tiff-pixeldata

C++: TIFF pixel data read/write interfaces and skeleton implementation