Improved Exception message when cannot read .obda file due to
unsupported tags
* Improved the factory method that creates CQIE with anew more onvineint
method that doesn't require to create lists everytime you creata query
body.
* Fixed issue that we geenrated Join(...) atoms when not needed. Now
Join is only used in the context of the left or irght ocmponents of a
leftJoin. Everywhere else, Join is redundant and no longer produced.