Added toBeDeleted to dataset model.

When a model is hidden set the toBeDeleted flag to 5 mins in the future
so that it can be cleaned up later.
After hiding a dataset remove the tile after 5 mins.
Added findToBeDeleted method to dataset model.
Script to call cleanCrontab on all to be deleted datasets.
Remove crontab when dataset.cleanCrontab is called.
make clean_crontabs handle asynchronicity
set toBeDeleted in subnav delete as well
extract RedisClient into its own module
parse string Date from JSON into real Date object
findToBeDeleted should use @find, not mongoose find

This is so we can get proper Dataset models
don't create a redis connection if we're cron
set toBeDeleted to null if we've successfully removed the crontab
@client.auth not Dataset...auth
script for cron to run when it's deleting datasets
Merge branch '20130802-deleted-dataset-cron-disable'