Extend date description to include hh:mm:ss

We need to be able to analyze corpora with time resolution below day (ex. for AMULEX project). This improvement would :

1. the possibility to add three meta-data to a doc : hour, minute, second
2. add hour, minute & second in the drop down of the phylomemy parameter panel so that we can analyze dynamics at the granularity of on of these units.
3. check that when choosing these units, the dates in the phylemomy vizualization are rightly labelled (for @karenkonou ?)