Move caching into shared methods.

```
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
```