Added creation of 'resources' subfolder in user data path to
CreateUserDataFoldersCommand if the folder isn't found.
Added functionality to obtain the path to resource file through a
ResourceUtil class that first checks whether the file exists in the user
data path. Encapsulated the AIR-only File API with an interface to not
hinder compilation of web builds.

Integrated this feature so far with IndexResourceLoader. Loading all
other resource files via this API will be the next step which then will
make resource file overriding possible.