tools (common/date_utils) handle timestamp and `in` + `delta2human`: regex used to parse datetimes has been improved to handle a unix time (which can be used with `+ <delta>` or `- <delta>`), and the `in <delta>` (e.g. `in 6 days`). `DEFAULT_DATETIME` has been removed as dateutil use current date by default, which is the expected behaviour. Add `delta2human` method which convert the difference of 2 unix times to a human friendly approximate text. rel 372

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