Separate polling of cart and queued Downloads

[patrick-austin]

Also reduces severity of the DownloadRepository logging, adds a log after prepareData returns the preparedId (INFO)

Closes #75

[kevinphippsstfc]

I feel like polling the queue every second is too much as in this case we don't have the problem of the potential user logouts like we do for the other poll. Probably once every 10 mins is enough. Perhaps it is even worth making this configurable so that we can set it low to speed up testing and then increase it in production?

[patrick-austin]

We can't make it configurable with the cron syntax, as the arguments provided to the @Schedule decorator have to be constants. We could make it configurable with an internal timer, similar to have it's done for the existing poll (either with a single last checked time applied outside the for loop or one for each Download within it). Or we could not use @Schedule and use the Timer class instead. Or just hardcode it to a different frequency.

[kevinphippsstfc]

OK, I think for now we should just go with setting it to 10 mins