extend dateTimeFormatString to hours, minute and seconds

[earnaud]

In one met use case, EAL sets as "categorical" an attribute containing hours at HH:MM:SS format.

According to EML documentation, this shall be set as an hour time format.

[clnsmth]

Hi @earnaud, template_table_attributes() guesses the column class beginning around line 223 (PR's to improve this code are welcome). If a column class is guessed incorrectly, the user should change it to the correct class. The "Date" class covers both dates and times and should work for HH:MM:SS.

[earnaud]

I think MetaShARK will need to get the separator specified (although I could check by myself some of the most common ones). I will check your code to try to detect any bug or so.