(ImageLoading) Added new method to get closest image size

(ImageLoading) Added new method to get closest image size

[Issue#]       N/A
[Problem]      No synchronous method to get closest image size.
Jpeg loader will give different size if requested, as it implements image scaling.
Want to have image actor size set to the natural size from creation, rather than
only after loading.
[Cause]        Not implemented
[Solution]
Changed signature of BitmapLoader header function to pass in ImageAttributes.
Changed meaning of header function - if a non-zero size is set, then the header
function should work out what size will be returned for the requested size and
orientation correction parameters (as would be done in the actual loader function)

refactored jpeg loader to write new header method to handle scaling and orientation
correction

Changed png header to account for cropping

[Verification] Build Repo

Change-Id: I1c9b814aafacff70f089df0735ab5bb6a108cfcc
Signed-off-by: David Steele <david.steele@partner.samsung.com>