add flags to `create-lab` command to set expiration date based on literals

[hellt]

In order to humanise the expiration date calculation it makes sense to set expiration date using the literals like:

-e 5h == 2 hours
-e 2d == 2 days
-e 3w == 3 weeks
-e 20d == 20 days

[hellt]

added in #13