Fix "size" URL parameter converion to be int value or "full" literal.

CacheManager expects value of "size" parameter in it�'s methods to be either
integer or str with value "full"(this was inferenced from
config['ALLOWED_SIZES']). The problem was that values that seems to be valid
(like str "200") weren't converted to integers and later failed the check
"size in config['ALLOWED_SIZES']". Fixed by using standard flask parameter
type conversion with extra route config for value "full".