#2 refactor exceptions

[Marin Dimitrov]

the present exception mechanism is not very consistent.
E.g. we need to:

- decide if we need more (fine grained) exceptions in
addition to SyncEx, InvalidModelEx, ParserEx

- decide if the present usage of the above exceptions
is always appropriate

see also
https://sourceforge.net/tracker/index.php?func=detail&aid=1228215&group_id=113501&atid=665349