Move caching into shared methods.

[Snuggle]

def addToCache(cacheURL, data, cacheLength):
    # Return True if added, return False if not
    pass

def removeFromCache(cacheURL):
    # Return True if removed, False if not
    pass

def getFromCache(cacheURL):
    # Return data or None
    pass

def cleanCache():
    # Calls removeFromCache
    pass