title: Convert timeunits to timestamps
body: <p>I did a simulation with simmer and I got an event log. The start and end of an activity are represented as time units.
  they look as follows:</p>
  <pre><code>|   start   |    end    |
  | --------- | --------  |
  |  5.658733 | 13.244381 |
  | 11.342792 | 13.583395 |
  | 12.000000 | 13.612889 |
  | 14.000000 | 14.000000 |
  ...
  | 2694.162  | 6699.370  |
  
  </code></pre>
  <p>I would like to convert these in timestamps. For that, I would like to determine an exact time and date of time at which the simulation started and convert all the following time units accordingly to timestamps that look like &quot;2020-01-02 11:23:00&quot;.
  I set the simulation to run until time unit 2700</p>
  <pre><code>run(until=2700)
  </code></pre>
  <p>As far as I understand this means the simulation runs for 1 week (7 days).</p>