Add natural langage support for scheduling

[rumdood]

Currently the bot requires dates and times to be given in specific formats so that it can correctly parse them (e.g. "yyyy-MM-dd HH:mm:ss[am/pm]"

This should be improved so that the user can specify a date/time like "tomorrow at noon" or "Friday afternoons at 3" and the bot can then deduce the correct date or CRON statement.

Examples:

"Tomorrow at noon" - Calculate the date for tomorrow and set the time to 12:00:00pm
"Friday afternoons at 3" - CRON statement of 0 0 15 * * 5
"Next Tuesday at 10am" - Calculate the date for the upcoming Tuesday and set the time to 10:00:00am