Get rid of IdentifiableTable in SlickDao

Hello Renato,

Looking at your latest changes, I was wondering: why is IdentifiableTable needed if you have to define queryById ? (btw I know the answer why you introduced queryById...)

If you remove the IdentifiableTable and let the dao define it's own add method, you can use any key you want (tuples as keys, multiple columns, ...).

So, here is a simple proposition: remove IdentifiableTable from SlickJdbcDao and define a new trait that extends SlickJdbcDao and use IdentifiableTable.