New files implementing an asynchronous cache.
Updated docs on example script
Fixed spelling error.  Removed unecessary code
Updated docs
Made changes in response to PR feedback
Use a more specific class for the caching client
Type 'callable' should include a string
Improve the method docs
HG-299 Remove article dependency on basePath attr.
don't send cb param when cb=0. this sidesteps the issue of having a param in params, for now at least. also do some ghetto concatenating when requesting a vignette background image
Merge pull request #5233 from Wikia/HG-299

HG-299 Remove article dependency on basePath attr.
Merge pull request #5234 from Wikia/PLATFORM-564

ThemeDesigner custom background images
adding isset() check

(cherry picked from commit b88497bbbcd011a27450251b558d9d8b0783a496)
Update method signatures and docs.  Simplify logic
Merge pull request #5045 from Wikia/AsyncCache

New files implementing an asynchronous cache.
Merge branch 'dev' into VideoSprint60