Fixed podspec for moved files
Added workspace and Podfile.lock now that pods are used
Made gif serializer strict and only supporting gif

Standard AFNetworking serializer not only assigns image, but also checks
for status codes, MIME types, and inflated images on background thread
before assigning. Loosing this behaviour on all images is unwanted, but
calling super would inflate gifs and cause which could interfere with
OLImage logic.