Booking date

[nus-se-bot]

Describe the bug
I am able to do booking at year 0000 or any past years

To Reproduce
Steps to reproduce the behavior:

1. addbooking c/1 ts/0000-02-23T14:30 n/3

Expected behavior
Should not be able to make a booking for last year or earlier

Screenshots

Additional context
Add any other context about the problem here.

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Reported by: @NgWeiXin
Severity: Medium

_{[original: nus-cs2103-AY1819S2/pe-dry-run#550]}

[lingyanhao]

This is more of an acceptance rather than a system test- indeed we might want to consider restricting the date range.

Currently, the system does not provide any guarantee on what dates should be accepted.

However, is becomes unclear what the "correct" threshold should be. More than a year ago? More than a month ago? More than a day ago? Anything into the past?