A bunch of updates

Added a new scenario to the Cron expression helper. This allows you to calculate the Cron expression for a job to run periodically but only within a restricted time frame. For example, if you wanted to run a job every 30 minutes but only during office hours this can show you the Cron expression to use.

There's new hash calculators for MD4, SHA256 and SHA512. These work just like the existing hash calculators. Also new is a Unix timestamp converter to convert readable dates to and from a standard Unix timestamp.